U.S. patent number 9,217,552 [Application Number 14/417,235] was granted by the patent office on 2015-12-22 for illumination device.
This patent grant is currently assigned to Sharp Kabushiki Kaisha, Tohoku University. The grantee listed for this patent is Sharp Kabushiki Kaisha, TOHOKU UNIVERSITY. Invention is credited to Katsunori Ehara, Yoshihiro Hashimoto, Yutaka Ishii, Takahiro Ishinabe, Yasuhisa Itoh, Tohru Kawakami, Toshiki Matsuoka, Kozo Nakamura, Yoshito Suzuki, Tatsuo Uchida, Yoshitaka Yamamoto.
United States Patent |
9,217,552 |
Uchida , et al. |
December 22, 2015 |
Illumination device
Abstract
A lighting device (100) includes: a surface light source (1); a
first lens (L1) having a first focal point (F1), the first lens
being provided on the light exit surface side of the surface light
source; and a second lens (L2) having a second focal point (F2),
the second lens being provided on a light exit surface side of the
first lens, the surface light source, the first lens, and the
second lens being configured such that a first virtual image (I1)
is formed by the first lens and a second virtual image (I2) is
formed by the second lens, wherein the first virtual image (I1) is
formed between the second focal point (F2) and the first lens, the
second focal point (F2) is on a side opposite to the light source
side relative to a predetermined focal position f', and at least
either of a light entry surface or a light exit surface of the
first lens or the second lens includes a non-revolution surface
(SO) as a lens surface, and a plurality of boundary lines (B1-B4)
whose curvatures vary discontinuously are provided in the
non-revolution surface.
Inventors: |
Uchida; Tatsuo (Sendai,
JP), Suzuki; Yoshito (Sendai, JP),
Kawakami; Tohru (Sendai, JP), Ishinabe; Takahiro
(Sendai, JP), Ehara; Katsunori (Sendai,
JP), Hashimoto; Yoshihiro (Osaka, JP),
Matsuoka; Toshiki (Osaka, JP), Nakamura; Kozo
(Osaka, JP), Itoh; Yasuhisa (Osaka, JP),
Yamamoto; Yoshitaka (Osaka, JP), Ishii; Yutaka
(Osaka, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Sharp Kabushiki Kaisha
TOHOKU UNIVERSITY |
Osaka-shi, Osaka
Sendai-shi, Miyagi |
N/A
N/A |
JP
JP |
|
|
Assignee: |
Sharp Kabushiki Kaisha (Osaka,
JP)
Tohoku University (Miyagi, JP)
|
Family
ID: |
49997078 |
Appl.
No.: |
14/417,235 |
Filed: |
July 2, 2013 |
PCT
Filed: |
July 02, 2013 |
PCT No.: |
PCT/JP2013/068124 |
371(c)(1),(2),(4) Date: |
January 26, 2015 |
PCT
Pub. No.: |
WO2014/017262 |
PCT
Pub. Date: |
January 30, 2014 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20150167924 A1 |
Jun 18, 2015 |
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Foreign Application Priority Data
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|
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Jul 27, 2012 [JP] |
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2012-167663 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
19/0014 (20130101); F21V 5/008 (20130101); F21K
9/60 (20160801); G02B 19/0061 (20130101); F21V
5/04 (20130101); F21Y 2115/10 (20160801) |
Current International
Class: |
F21V
5/04 (20060101); F21K 99/00 (20100101); F21V
5/00 (20150101); G02B 19/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2009-004276 |
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Jan 2009 |
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JP |
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2008/016908 |
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Feb 2008 |
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WO |
|
Primary Examiner: Bowman; Mary Ellen
Attorney, Agent or Firm: Keating & Bennett, LLP
Claims
The invention claimed is:
1. A lighting device, comprising: a surface light source having a
light exit surface; a first lens having a first focal point, the
first lens being provided on the light exit surface side of the
surface light source; and a second lens having a second focal
point, the second lens being provided on a light exit surface side
of the first lens, the surface light source, the first lens, and
the second lens being configured such that a first virtual image is
formed by the first lens and a second virtual image is formed by
the second lens, wherein the first virtual image is formed between
the second focal point and the first lens, the second focal point
is on a side opposite to the surface light source relative to a
position which is distant from a principal point of the second lens
by a predetermined focal length f', the predetermined focal length
f' satisfies I'=(D/(.epsilon.+D))f' where I' is the distance
between the principal point of the second lens and a position of
the first virtual image, D is an effective diameter of the second
lens, and .epsilon. is a light source size factor which is either
one of a size of the light exit surface of the surface light source
or an arrangement pitch of a plurality of light-emitting elements
included in the surface light source, and at least either of a
light entry surface or a light exit surface of the first lens or
the second lens includes a non-revolution surface as a lens
surface, and a plurality of non-concentric boundary lines whose
curvatures vary discontinuously are provided in the non-revolution
surface.
2. The lighting device of claim 1, wherein at least one of the
plurality of boundary lines extends outward from a center of the
non-revolution surface.
3. The lighting device of claim 2, wherein the non-revolution
surface has three or more unit faces separated by the plurality of
boundary lines, the three or more unit faces being rotationally
symmetrically arranged about an axis extending through the center
of the non-revolution surface.
4. The lighting device of claim 3, wherein x-direction and
y-direction which are orthogonal to each other in a plane which is
perpendicular to an optical axis direction are defined, and in at
least one of the three or more unit faces, a curvature in the
x-direction and a curvature in the y-direction are different from
each other.
5. The lighting device of claim 4, wherein at least one of the
three or more unit faces is a free curved surface.
6. The lighting device of claim 1, wherein when the non-revolution
surface forms a light exit surface of the first lens or the second
lens, the non-revolution surface includes two convex curved
surfaces which are adjacent to each other with one of the plurality
of boundary lines formed between the two convex curved surfaces,
and the boundary line formed between the two convex curved surfaces
is a trough line, and when the non-revolution surface forms a light
entry surface of the first lens or the second lens, the
non-revolution surface includes two concave curved surfaces which
are adjacent to each other with one of the plurality of boundary
lines formed between the two concave curved surfaces, and the
boundary line formed between the two concave curved surfaces is a
ridge line.
7. The lighting device of claim 1, wherein the light source size
factor c is not less than a minimum pitch of in-plane intensity
unevenness of the light exit surface.
8. The lighting device of claim 1, wherein the first virtual image
is formed between the first focal point and the first lens, and the
second virtual image is formed between the second focal point and
the second lens.
9. The lighting device of claim 8, wherein the first virtual image
and the second virtual image are formed between an effective focal
point of the first lens and the second lens and the first lens.
10. The lighting device of claim 8, further comprising a second
optical system provided on a light exit side of a first optical
system that includes the first lens and the second lens.
11. The lighting device of claim 10, wherein the second optical
system includes a concave lens which is the closest to the first
optical system and a convex lens which is next to the concave lens
and is the second closest to the first optical system.
12. The lighting device of claim 1, wherein the non-revolution
surface is provided at the light exit surface of the second lens,
and the light exit surface of the first lens and a light entry
surface of the second lens are joined together.
13. The lighting device of claim 12, wherein the first lens and the
second lens are formed of a resin by integral molding.
14. The lighting device of claim 9, wherein a lens surface of the
first lens facing on the surface light source is a concave curved
surface, and a width h of a range of a position at which the light
exit surface can be placed is represented by the following formula:
h.ltoreq.2 (d(2R-d)) where d is a distance along an optical axis
from the light exit surface of the surface light source to the
concave curved surface of the first lens, and R is a radius of
curvature of the concave curved surface of the first lens.
15. The lighting device of claim 9, wherein a<f/2 is satisfied
where a is a distance from a principal point of an optical lens
section including the first lens and the second lens to the light
exit surface, and f is a distance from the principal point to a
focal position of the optical lens section.
Description
TECHNICAL FIELD
The present invention relates to a lighting device which includes a
surface emitting element.
BACKGROUND ART
A known example of common lighting devices is a lighting device 900
shown in FIG. 54.
The lighting device 900 has a collimating optical system LC which
includes a meniscus lens L1 and an aspherical lens L2 and is
configured such that a LED light source 10 is placed at the focal
position of this optical system as shown in FIG. 54.
Here, light emitted from a point on the optical axis AX of the LED
light source 10 is collimated light which is parallel to the
optical axis AX as shown in FIG. 54. On the other hand, since the
LED light source 10 is a surface light source rather than a point
light source, there is light emitted from a location away from the
optical axis AX. The light emitted from a location away from the
optical axis AX travels in a direction which is different from the
optical axis AX and therefore reaches a place which is different
from that the light emitted from a point on the optical axis AX
reaches. Thus, there is a problem that illuminance uniformity is
not achieved across the illuminated surface.
Moreover, since the meniscus lens L1 and the LED light source 10
are distant from each other, there is a probability that light
emitted from the LED light source 10 at a large angle is not
incident upon the meniscus lens L1.
Patent Documents 1 and 2 disclose light sources which can utilize
almost all of light emitted from a LED emitter.
The light source disclosed in Patent Document 1 has a LED emitter,
an inner lens enclosing the LED emitter, and a meniscus lens
covering these components. The light source disclosed in Patent
Document 2 has a LED emitter and a meniscus lens covering the light
emitter with a gap provided therebetween. In these light sources, a
virtual image Vl.sub.1 formed by an inner surface of the meniscus
lens is produced at a position outer than the LED emitter (on the
light exit surface side of the lens).
As described above, when the virtual image Vl.sub.1 formed by the
inner surface of the meniscus lens is produced at a position outer
than the LED emitter, almost all of light emitted from the LED
emitter is incident upon the meniscus lens. This improves the light
utilization efficiency of the light emitted from the LED
emitter.
CITATION LIST
Patent Literature
Patent Document 1: Specification of U.S. Pat. No. 7,798,678 Patent
Document 2: WO 2008/016908 Patent Document 3: Japanese Laid-Open
Patent Publication No. 2009-4276
SUMMARY OF INVENTION
Technical Problem
However, in the light sources of Patent Documents 1 and 2,
achieving the uniformity of the illuminated surface is not
considered although it is possible to utilize almost all of light
emitted from the LED emitter as described above. For example, such
a problem can occur that light emitted from a location away from
the optical axis of the lens illuminates a region which is
different from that the light emitted from a location on the
optical axis illuminates, so that the uniformity of the illuminated
surface cannot be achieved.
Further, there has been the use of illuminating a region of a
non-circular shape using a lighting device, and in many of
conventional examples, light emitted from a light source is
partially blocked in order to control the shape of the illumination
region. Specifically, in order to realize a non-circular (e.g.,
quadrangular) illumination region, for example, a light blocking
plate which has an aperture (opening), or a blade member provided
near a light exit portion of the lighting device, is used. However,
there is a problem that such solutions deteriorate the light
utilization efficiency.
For example, Patent Document 3 discloses a spotlight which is
capable of forming a non-circular illumination region using a
surface light source of a quadrangular or trapezoidal shape.
However, this spotlight has a blocking plate which has an opening
adapted to the spot shape in the light source, and therefore, the
light utilization efficiency decreases.
Thus, forming a non-circular illumination region without decreasing
the light utilization efficiency has been demanded. Lighting
devices of this type are suitably used in the fields of stage
lighting for, for example, providing a spotlight of a different
(non-circular) shape, such as quadrangular, triangular, etc.
The present invention was conceived for the purpose of solving the
above problems. An object of the present invention is to provide a
lighting device which is capable of forming an illumination region
of a different shape while improving the light utilization
efficiency.
Solution to Problem
A lighting device according to an embodiment of the present
invention includes: a surface light source having a light exit
surface; a first lens having a first focal point, the first lens
being provided on the light exit surface side of the surface light
source; and a second lens having a second focal point, the second
lens being provided on a light exit surface side of the first lens,
the surface light source, the first lens, and the second lens being
configured such that a first virtual image is formed by the first
lens and a second virtual image is formed by the second lens,
wherein the first virtual image is formed between the second focal
point and the first lens, the second focal point is on a side
opposite to the surface light source relative to a position which
is distant from a principal point of the second lens by a
predetermined focal length f', the predetermined focal length f'
satisfies l'=(D/(.epsilon.+D))f' where l' is the distance between
the principal point of the second lens and a position of the first
virtual image, D is an effective diameter of the second lens, and
.epsilon. is a light source size factor which is either one of a
size of the light exit surface of the surface light source or an
arrangement pitch of a plurality of light-emitting elements
included in the surface light source, and at least either of a
light entry surface or a light exit surface of the first lens or
the second lens includes a non-revolution surface as a lens
surface, and a plurality of non-concentric boundary lines whose
curvatures vary discontinuously are provided in the non-revolution
surface.
In one embodiment, at least one of the plurality of boundary lines
extends outward from a center of the non-revolution surface.
In one embodiment, the non-revolution surface has three or more
unit faces separated by the plurality of boundary lines, the three
or more unit faces being rotationally symmetrically arranged about
an axis extending through the center of the non-revolution
surface.
In one embodiment, x-direction and y-direction which are orthogonal
to each other in a plane which is perpendicular to an optical axis
direction are defined, and in at least one of the three or more
unit faces, a curvature in the x-direction and a curvature in the
y-direction are different from each other.
In one embodiment, at least one of the three or more unit faces is
a free curved surface.
In one embodiment, when the non-revolution surface forms a light
exit surface of the first lens or the second lens, the
non-revolution surface includes two convex curved surfaces which
are adjacent to each other with one of the plurality of boundary
lines formed between the two convex curved surfaces, and the
boundary line formed between the two convex curved surfaces is a
trough line, and when the non-revolution surface forms a light
entry surface of the first lens or the second lens, the
non-revolution surface includes two concave curved surfaces which
are adjacent to each other with one of the plurality of boundary
lines formed between the two concave curved surfaces, and the
boundary line formed between the two concave curved surfaces is a
ridge line.
In one embodiment, the light source size factor .epsilon. is not
less than a minimum pitch of in-plane intensity unevenness of the
light exit surface.
In one embodiment, the first virtual image is formed between the
first focal point and the first lens, and the second virtual image
is formed between the second focal point and the second lens.
In one embodiment, the first virtual image and the second virtual
image are formed between an effective focal point of the first lens
and the second lens and the first lens.
In one embodiment, a second optical system is further provided on a
light exit side of a first optical system that includes the first
lens and the second lens.
In one embodiment, the second optical system includes a concave
lens which is the closest to the first optical system and a convex
lens which is next to the concave lens and is the second closest to
the first optical system.
The non-revolution surface is provided at the light exit surface of
the second lens, and the light exit surface of the first lens and a
light entry surface of the second lens are joined together.
In one embodiment, the first lens and the second lens are formed of
a resin by integral molding.
In one embodiment, a lens surface of the first lens facing on the
surface light source is a concave curved surface, and a position
range h at which the light exit surface can be placed is
represented by the following formula: h.ltoreq.2 (d(2R-d)) where d
is a distance along an optical axis from the light exit surface of
the surface light source to the concave curved surface of the first
lens, and R is a radius of curvature of the concave curved surface
of the first lens.
In one embodiment, a<f/2 is satisfied where a is a distance from
a principal point of an optical lens section including the first
lens and the second lens to the light exit surface, and f is a
distance from the principal point to a focal position of the
optical lens section.
In a lighting device according to an embodiment, an optical lens
section formed by a plurality of optical lenses is provided on a
light extraction side of a light emission section. In the optical
lens section, the focal position of each optical lens is present on
a side opposite to a surface facing on the light emission section
relative to a virtual image formed by the optical lens. According
to this configuration, the virtual image formed by each lens can
occur at a position near the light emission section.
This configuration enables light emitted from the center of the
light emission section which is on the optical axis of the optical
lens section and light emitted from a location away from the center
of the light emission section to outgo from the optical lens
section with generally equal angular distributions. Therefore, both
the light emitted from the center of the light emission section and
the light emitted from a location away from the center of the light
emission section can equally illuminate the entirety of a
predetermined illumination region, so that the uniformity of the
illumination region can be significantly improved.
Furthermore, since the light emitted from the center of the light
emission section and the light emitted from a location away from
the center of the light emission section can outgo from the optical
lens section with generally equal angular distributions,
substantially no part of the light fails to reach the optical lens
section, and as a result, high light utilization efficiency can be
achieved.
Thus, it is possible to utilize almost all of the light emitted
from the light emission section, and high light utilization
efficiency is achieved, while light emitted from different
locations of the light emission section can be projected onto
generally equal illumination regions, leading to a distinguishing
effect that the uniformity of the illumination region can be
significantly improved.
To achieve an effect which is generally equal to the above, for
example, in a lighting device where a lens section formed by a
plurality of optical lenses is provided on a light projection
surface side of the light emission section, an effective focal
position determined by totalizing the focal points of the
respective optical lenses that are constituents of the optical lens
section may be present on a side opposite to surfaces of all the
virtual images facing on the light emission section relative to the
respective virtual images formed by the optical lenses.
The above-described configuration also enables the virtual image
formed by each lens to occur at a position near the light emission
section. Therefore, it is possible to utilize almost all of the
light emitted from the light emission section, and high light
utilization efficiency is achieved, while light emitted from
different locations of the light emission section can be projected
onto generally equal illumination regions, leading to a
distinguishing effect that the uniformity of the illumination
region can be significantly improved.
Furthermore, according to the above-described configuration, since
an effective focal position determined by totalizing the focal
points of the respective optical lenses that are constituents of
the optical lens section is present on a side opposite to surfaces
of all the virtual images facing on the light emission section
relative to the respective virtual images formed by the optical
lenses, the virtual images formed by the respective lenses can
occur at positions which are still closer to the light emission
section. Therefore, the angle of the light outgoing from the
optical lens section can be expanded, and thus, the uniformity of a
larger illumination region can be significantly improved.
Where the above-described optical lens section is the first optical
lens section, the second optical lens section may be provided on
the light exit side of the first optical lens section.
According to the above-described configuration, the light exit
angle of the light outgoing from the first optical lens section can
be changed by the second optical lens section. That is, the light
exit angle of the light outgoing from the first optical lens
section can be narrowed or expanded by changing the optical
characteristics of the second optical lens section.
Thus, the area of the light illumination region can be freely
changed by controlling the design of the second optical lens
section.
The above-described second optical lens section may be configured
such that a lens which is the closest to the first optical lens
section is a concave lens, and a lens which is the second closest
to the first optical lens section a convex lens.
Such a combination of a concave lens and a convex lens enables
correction of the aberrations occurring in the respective lenses,
and therefore, the characteristics of light outgoing from the first
optical lens section can be kept undamaged.
Thus, the light exit angle of the light outgoing from the first
optical lens section is adjustable, and it is possible to utilize
almost all of the light emitted from the light emission section, so
that high light utilization efficiency is achieved. Meanwhile,
light emitted from different locations of the light emission
section can be projected onto generally equal illumination regions,
leading to a distinguishing effect that the uniformity of the
illumination region can be significantly improved.
In the above-described optical lens section, part of the interface
of the above-described respective lenses may be integrally
formed.
Since part of the respective lenses that are constituents of the
optical lens section is thus integrally formed, alignment of the
emission surface of the light emission section and the optical lens
section can be easily achieved.
Further, fixing of the light emission section and the optical lens
section can also be easily achieved.
Possible methods of forming an integral structure of two lenses
include integral molding with the use of a resin and adhesion with
the use of an adhesive agent. The two lenses may be formed of a
resin by integral molding.
In this case, since the two lenses are formed of a resin by
integral molding, the molding cycles in formation of the optical
lens section can be reduced from two cycles (in the case of two
lenses) to one cycle. Accordingly, the manufacturing cost can be
reduced.
Of the lenses that are constituents of the above-described optical
lens section, in the first optical lens where a lens surface which
is the closest to the light emission section is a concave surface
which is concaved against the light emission section, h.ltoreq.2
(d(2R-d)) may hold where d is the distance from the emission
surface of the light emission section to the interface of the first
optical lens on the optical axis, R is the radius of curvature of
the inner lens of the first optical lens, and h is the arrangement
range on the optical axis of the light emission section. Thus,
since the arrangement range h of the light emission section is set
as described above, all of the light emitted from the light
emission section is brought into the first optical lens, so that
the light utilization efficiency can be improved.
Where the distance from the principal point of the above-described
optical lens section to the emission surface of the light emission
section is a and the distance from the principal point of the
optical lens section to the focal position is f, a<f/2 may be
satisfied.
By thus making the distance a from the principal point of the
optical lens section to the emission surface of the light emission
section shorter than a half of the distance f from the principal
point of the optical lens section to the focal position, the
virtual image position can always be relatively close to the
optical lens section as compared with the focal position of the
optical lens section.
The above-described light emission section may include a plurality
of light emitters. In this case, the plurality of light emitters
are arranged over the emission surface of the light emission
section. Even when the light emitters emit varying amounts of
light, light is projected such that these variations are canceled
at the illuminated surface. That is, light emitted from respective
ones of the light emitters are projected onto the same illumination
region, and therefore, even when the light emitters emit varying
amounts of light, this variation is canceled.
Advantageous Effects of Invention
According to a lighting device of an embodiment of the present
invention, it is possible to illuminate a region of a non-circular
shape while improving the illuminance uniformity.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 A general configuration diagram of a lighting device
according to an embodiment of the present invention.
FIG. 2 A general configuration diagram of a lighting device
according to an embodiment of the present invention.
FIG. 3 A diagram showing a light ray behavior in the lighting
device shown in FIG. 2.
FIG. 4 (a) is a diagram showing a general configuration of the
lighting device shown in FIG. 2. (b) is a diagram showing a general
configuration of a lighting device of a comparative example.
FIG. 5 (a) is a diagram showing a light ray behavior of the
lighting device shown in FIG. 4(a). (b) is a diagram showing a
light ray behavior of the lighting device shown in FIG. 3(b).
FIG. 6 A diagram showing an example where an evaluation plane is 1
m distant from the lighting device.
FIG. 7 A chart showing the illumination intensity distribution at
the evaluation plane shown in FIG. 6.
FIG. 8 A graph showing the relationship between the relative
illuminance in the illumination intensity distribution shown in
FIG. 7 and the illumination position.
FIG. 9 (a) is a diagram showing an example where a plurality of
minute light-emitting surfaces are arranged. (b) is a diagram
showing an example where some of the minute light-emitting surfaces
are dark. (c) is a chart showing the illumination intensity
distribution in the case of FIG. 9(b).
FIG. 10 A diagram showing the relationship between the lighting
device and evaluation planes.
FIG. 11 (a) is a chart showing a two-dimensional illuminance
distribution at the evaluation plane a shown in FIG. 10. (b) is a
chart showing a two-dimensional illuminance distribution at the
evaluation plane b shown in FIG. 10.
FIG. 12 (a) illustrates optical lens conditions under which the
lighting device shown in FIG. 1 was actually manufactured. (b) is a
chart showing the state of light projection in an illumination
region formed when the lighting device shown in FIG. 1 was actually
manufactured.
FIG. 13 (a) illustrates optical lens conditions under which the
lighting device shown in FIG. 2 was actually manufactured. (b) is a
chart showing the state of light projection in an illumination
region formed when the lighting device shown in FIG. 2 was actually
manufactured.
FIG. 14 A general configuration diagram of a lighting device
according to another embodiment of the present invention.
FIG. 15 An enlarged view of the major portion B of the lighting
device shown in FIG. 14.
FIG. 16 A chart showing the illumination intensity distribution in
the lighting device shown in FIG. 14.
FIG. 17 A general configuration diagram of a lighting device
according to still another embodiment of the present invention.
FIG. 18 An enlarged view of major portion B of the lighting device
shown in FIG. 17.
FIG. 19 A chart showing the illumination intensity distribution in
the lighting device shown in FIG. 17.
FIG. 20 A general configuration diagram of a lighting device
according to still another embodiment of the present invention.
FIG. 21 A general configuration diagram of a lighting device
according to still another embodiment of the present invention.
FIG. 22 A diagram showing the relationship between the lighting
device and the evaluation plane.
FIG. 23 A chart showing the illumination intensity distribution at
the evaluation plane shown in FIG. 22.
FIG. 24 A diagram showing the relationship between the lighting
device and the evaluation plane.
FIG. 25 A chart showing the illumination intensity distribution at
the evaluation plane shown in FIG. 24.
FIG. 26 A diagram for illustrating the placement range of a light
emission section in the lighting device of the present
invention.
FIG. 27 A diagram showing the relationship between the focal points
of the first lens and the second lens and the positions of virtual
images formed by respective lenses. (a) (e) show alternative
arrangement relationships.
FIG. 28 A chart showing illuminance unevenness occurring across a
light exit surface of a surface light source.
FIG. 29 A diagram showing the positional relationship between the
reference focal point f' and the focal point F2 of the second
lens.
FIG. 30 (a) is a diagram for illustrating a deep focus state. (b)
is a diagram for illustrating an application to a lighting
device.
FIG. 31 A diagram for explaining that the position of the reference
focal point f' varies according to the light source size factor
(permissible circle of confusion) .epsilon..
FIG. 32 Diagrams for illustrating the repetition pitch in a surface
light source. (a) shows a case where LEDs of three colors are used.
(b) shows a case where LED columns of two different characteristics
are arranged.
FIG. 33 Diagrams showing a lighting device according still another
embodiment of the present invention. (a) is a perspective view
showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view). (c) is a
perspective view of the second lens.
FIG. 34 (a) shows an illuminance distribution achieved by the
lighting device shown in FIGS. 33. (b) and (c) show the shape of
the illumination region.
FIG. 35 Diagrams showing a lighting device according still another
embodiment of the present invention. (a) is a perspective view
showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view). (c) is a
perspective view of the second lens.
FIG. 36 (a) shows an illuminance distribution achieved by the
lighting device shown in FIGS. 35. (b) and (c) show the shape of
the illumination region.
FIG. 37 Diagrams showing a lighting device according to still
another embodiment of the present invention. (a) is a perspective
view showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view). (c) is a
perspective view of the second lens.
FIGS. 38 (a-1) and (b-1) are perspective views showing specific
lens shapes of the lighting device shown in FIGS. 37. (a-2) and
(b-2) show the shape of illumination regions in the case where the
lenses shown in (a-1) and (b-1), respectively, are used.
FIG. 39 Diagrams showing a lighting device according to still
another embodiment of the present invention. (a) is a perspective
view showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view). (c) is a
perspective view of the second lens.
FIG. 40 (a) shows an illuminance distribution achieved by the
lighting device shown in FIG. 39. (b) shows the shape of an
illumination region.
FIG. 41 Diagrams showing a lighting device according to still
another embodiment of the present invention. (a) is a perspective
view showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view). (c) is a
perspective view of the second lens.
FIG. 42 (a) shows an illuminance distribution achieved by the
lighting device shown in FIG. 41. (b) shows the shape of an
illumination region.
FIG. 43 Diagrams showing a lighting device according to still
another embodiment of the present invention. (a) is a perspective
view showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view).
FIG. 44 (a) shows an illuminance distribution achieved by the
lighting device shown in FIG. 43. (b) shows the shape of an
illumination region.
FIG. 45 Diagrams showing a lighting device according to a variation
of the embodiment shown in FIG. 43. (a) is a perspective view
showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view).
FIG. 46 (a) shows an illuminance distribution achieved by the
lighting device shown in FIG. 45. (b) shows the shape of an
illumination region.
FIG. 47 Diagrams showing a lighting device according to still
another embodiment of the present invention. (a) is a perspective
view showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view).
FIG. 48 (a) shows an illuminance distribution achieved by the
lighting device shown in FIG. 47. (b) and (c) show the shape of the
illumination region.
FIG. 49 Diagrams showing a lighting device according to a variation
of the embodiment shown in FIG. 47. (a) is a perspective view
showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view). (c) is a plan
view showing the second lens.
FIG. 50 (a) shows an illuminance distribution achieved by the
lighting device shown in FIGS. 49. (b) and (c) show the shape of
the illumination region.
FIG. 51 Diagrams showing a lighting device according to still
another embodiment of the present invention. (a) is a perspective
view showing a portion near a light source section of the lighting
device. (b) is a cross-sectional view (side view). (c) is a
perspective view of the second lens.
FIG. 52 Side views showing design size examples of the optical lens
shown in FIG. 51. (a) shows the entire lens. (b) is an enlarged
view of the first lens portion that is provided on the light source
side.
FIG. 53 (a) shows an illuminance distribution achieved by the
lighting device shown in FIG. 51. (b) shows the shape of the
illumination region.
FIG. 54 A general configuration diagram of a conventional lighting
device.
DESCRIPTION OF EMBODIMENTS
Hereinafter, embodiments of the present invention are described
with reference to the drawings, although the present invention is
not limited to these embodiments.
Embodiment 1
FIG. 1 and FIG. 2 are diagrams showing the general configuration of
a lighting device 11 according to the present embodiment.
FIG. 3 is a diagram showing the state of light projection in the
lighting device 11 shown in FIG. 2.
(Configuration of Lighting Device) . . . FIGS. 1, 2, and 3
As shown in FIG. 1, the lighting device 11 includes a light source
(light emission section) 1 and an optical lens section 2 provided
on the optical axis AX on the light exit surface side, which is the
light extraction side, of the light source 1. The lighting device
11 is configured such that light produced by the light source 1 is
projected through the optical lens section 2.
The light source 1 includes a LED emitter. The LED emitter is a
surface light emitter which is capable of surface emission. Note
that it is not limited to the LED emitter so long as it is a
surface light emitter which is capable of surface emission.
The optical lens section 2 includes two optical lenses L1, L2. From
the side closer to the light source 1, the optical lens L1 (or
"first lens L1") and the optical lens L2 (or "second lens L2") are
arranged in this order. Note that the optical lenses L1, L2 are
arranged such that the centers of the lenses are on the optical
axis AX.
The optical lens L1 has a diameter which is at least greater than
the maximum width of the emission surface of the light source 1. A
surface of the optical lens L1 on the light source 1 side has a
concave surface shape.
The optical lens L2 has a diameter which is at least greater than
the maximum diameter of the optical lens L1 that is the first
optical lens. The light exit surface side of the optical lens L2
has a convex shape.
Now, the focal positions of the optical lenses L1, L2 and virtual
images formed after passage through the optical lenses L1, L2 are
described.
The focal position of the optical lens L1 is f1 (also referred to
as "focal point F1"). A virtual image which is formed by passage of
light from the light source 1 through the optical lens L1 is a L1
virtual image (also referred to as "virtual image I1"). The focal
position of the optical lens L2 is f2 (also referred to as "focal
point F2"). A virtual image which is formed by passage of light
from the L1 virtual image formed by the optical lens L1 through the
optical lens L2 is a L2 virtual image (also referred to as "virtual
image I2"). The effective focal position of the optical lenses L1,
L2 is f1+f2 (also referred to as "effective focal point
F(1+2)").
In the lighting device 11 shown in FIG. 1, the optical lens section
2 is designed such that the focal points f1, f2 of the optical
lenses L1, L2 that are constituents of the optical lens section 2
are present on a side opposite to surfaces of corresponding virtual
images (L1 virtual image, L2 virtual image) facing on the light
source 1 relative to the respective virtual images formed by the
optical lenses L1, L2 (L1 virtual image, L2 virtual image). In this
configuration, the first virtual image I1 is formed between the
focal point f1 and the lens L1, and the second virtual image I2 is
formed between the focal point f2 and the lens L2.
A lighting device 11 which is based on an alternative design of the
present embodiment includes a light source (light emission section)
1 and an optical lens section 2 which is placed on the optical axis
AX on the light exit surface side of the light source 1 as shown in
FIG. 2. The lighting device 11 is configured such that light
produced by the light source 1 is projected through the optical
lens section 2.
The light source 1 includes a LED emitter. The LED emitter is a
surface light emitter which is capable of surface emission. Note
that it is not limited to the LED emitter so long as it is a
surface light emitter which is capable of surface emission.
The optical lens section 2 includes two optical lenses, the first
optical lens L1 and the second optical lens L2. From the side
closer to the light source 1, the optical lens L1 and the optical
lens L2 are arranged in this order. Note that the optical lenses
L1, L2 are arranged such that the centers of the lenses are on the
optical axis AX.
The optical lens L1 has a diameter which is at least greater than
the maximum width of the emission surface of the light source 1. A
surface of the optical lens L1 on the light source 1 side has a
concave surface shape.
The optical lens L2 has a diameter which is at least greater than
the maximum diameter of the optical lens L1 that is the first
optical lens. The light exit surface side of the optical lens L2
has a convex shape.
Now, the focal positions of the optical lenses L1, L2 and virtual
images formed after passage through the optical lenses L1, L2 are
described.
The focal position of the optical lens L1 is f1. A virtual image
which is formed by passage of light from the light source 1 through
the optical lens L1 is a L1 virtual image. The focal position of
the optical lens L2 is f2. A virtual image which is formed by
passage of light from the L1 virtual image formed by the optical
lens L1 through the optical lens L2 is a L2 virtual image. The
effective focal position of the optical lenses L1, L2 is f1+f2.
In the lighting device 11 shown in FIG. 2, the optical lens section
2 is designed such that the effective focal position f1+f2 of the
focal points f1, f2 of the optical lenses L1, L2 that are
constituents of the optical lens section 2 is present on a side
opposite to surfaces of all the virtual images (L1 virtual image,
L2 virtual image) facing on the light source 1 relative to the
respective virtual images formed by the optical lenses L1, L2 (L1
virtual image, L2 virtual image). In this configuration, the L1
virtual image and the L2 virtual image are formed between the
effective focal position f1+f2 of the lens L1 and the lens L2 and
the lens L1.
In the lighting device 11 in which the focal positions of the
optical lenses L1, L2 and virtual images formed after passage
through the optical lenses L1, L2 are in the relationship shown in
FIG. 2, all of light rays from the emission surface of the light
source 1 are guided to the optical lens section 2 as shown in FIG.
3 so that light can be efficiently projected onto a surface to be
illuminated. That is, according to the lighting device 11 that has
the above-described configuration, both high light utilization
efficiency and improved uniformity of the illuminated surface can
be achieved.
Hereinafter, the above-described effects achieved by the lighting
device 11 that has the above-described configuration are described
in detail.
Points of Present Embodiment
FIGS. 4 and 5
FIG. 4(a) is a model diagram for the focal positions of the optical
lenses L1, L2, and the L1 virtual image and the L2 virtual image
which are formed after passage through the optical lenses L1, L2,
respectively, in the lens configuration of the lighting device 11
of FIG. 2 (two-lens configuration). FIG. 4(b) is a model diagram
for the focal positions of the optical lenses L1, L2, and the L1
virtual image and the L2 virtual image which are formed after
passage through the optical lenses L1, L2, respectively, in an
alternative form.
In the lighting device 11 that has the above-described
configuration, as shown in FIG. 4(a), the optical lens section 2 is
designed such that, with respect to the position of the light
source, the focal positions f1, f2 of the optical lenses L1, L2 and
the effective focal position f1+f2 are present on a side opposite
to the light source side relative to the positions of virtual
images formed by the optical lenses L1, L2 (L1 virtual image, L2
virtual image).
In the above-described configuration, virtual images formed by the
optical lenses L1, L2 (L1 virtual image, L2 virtual image) are
formed relatively near the light source. Here, light which has
passed through a plurality of lenses (optical lenses L1, L2) can be
regarded as outgoing of light from a virtual image formed by the
last lens (in FIG. 4(a), L2 virtual image). Therefore, formation of
the L2 virtual image near the light source can lead to the effect
such as shown in FIG. 5(a).
FIG. 5(a) shows the routes of light emitted from the center of the
light source (thin lines in FIG. 5(a)) and light emitted from the
upper edge of the light source (thick lines in FIG. 5(a)) in the
lens configuration shown in FIG. 4(a). Here, the center of the
light source refers to a portion which is on the optical axis AX
that passes through the center of the optical lens section 2.
As seen from FIG. 5(a), in the case of the lens configuration shown
in FIG. 4(a), the light emitted from the center of the light source
and the light emitted from the upper edge of the light source outgo
from the optical lens section 2 with generally equal angular
distributions. Thus, according to the lens configuration shown in
FIG. 4(a), both the light emitted from the center of the light
source and the light emitted from the upper edge of the light
source can equally illuminate the entirety of a predetermined
illumination region, so that the uniformity of the illumination
region can be improved.
On the other hand, in the lens configuration of the alternative
form, as shown in FIG. 4(b), the L2 virtual image is formed by the
second optical lens L2 at a relatively distant position, and the L2
virtual image does not occur between the optical lens L2 and its
focal position f2 (this aspect is different from the configuration
shown in FIG. 4(a)). The focal position f2 of the optical lens L2
is placed at a position which is relatively close to the L1 virtual
image. In this configuration, the L2 virtual image occurs at a
position which is more distant from the light source than the focal
position f2 of the optical lens L2, sometimes leading to the result
such as shown in FIG. 5(b).
Note that, however, as will be described later, even when the L2
virtual image is distant from the light source 1, the uniformity in
illuminance across the illumination region can be improved so long
as the optical system is configured such that the L1 virtual image
is at least formed on the light source side relative to the focal
position f2 of the optical lens L2 and, meanwhile, the virtual
image I1 formed by the optical lens L1 and the focal position f2 of
the optical lens L2 are away from the light source 1 by a
predetermined distance or more as will be described later.
FIG. 5(b) shows an example of the routes of light emitted from the
center of the light source (thin lines in FIG. 5(b)) and light
emitted from the upper edge of the light source (thick lines in
FIG. 5(b)) in the case where the L1 virtual image is formed near
the light source in the lens configuration of FIG. 4(b). In the
example shown in FIG. 5(b), the light emitted from the center of
the light source and the light emitted from the upper edge of the
light source outgo from the optical lens L2 with different angular
distributions (this aspect is different from the case of FIG.
5(a)). With such a characteristic, light emitted from different
locations of the light source illuminate different ranges, and
therefore, there is a probability that the uniformity of the
illumination region cannot be achieved.
As described above, in the above-described configuration shown in
FIG. 4(a), the focal positions f1, f2 of the optical lenses L1, L2
which are provided on the light exit surface side of the light
source are provided at distant positions behind the L1 virtual
image and the L2 virtual image formed by the optical lenses L1, L2
(in a direction opposite to the lens emission side). This
arrangement enables relatively moving the light source and the
virtual image positions so as to be closer to the optical lenses
L1, L2.
In such a configuration, light emitted from the center of the light
source which is on the optical axis of the optical lens section and
light emitted from a location away from the center of the light
source are allowed to outgo particularly toward the optical lens L1
of the optical lens section 2 with generally equal angular
distributions. This enables both the light emitted from the center
of the light source and the light emitted from a location away from
the center of the light source to equally illuminate the entirety
of a predetermined illumination region, so that the illuminance
uniformity across the illumination region can be improved.
Furthermore, since the light emitted from the center of the light
source and the light emitted from a location away from the center
of the light source are allowed to outgo toward the optical lens
section with generally equal angular distributions, substantially
no part of the light fails to reach the optical lens section 2, and
as a result, high light utilization efficiency can be achieved.
Thus, it is possible to utilize almost all of the light emitted
from the light source, and high light utilization efficiency is
achieved, while light emitted from different locations of the light
source can be projected onto generally equal illumination regions.
This significantly improves the uniformity of the illumination
region.
Furthermore, since the focal points f1, f2 of the optical lenses
L1, L2 and the effective focal position f1+f2 are present on a side
opposite to surfaces of all the virtual images (L1 virtual image,
L2 virtual image) facing on the light source 1 relative to the
respective virtual images formed by the optical lenses L1, L2 (L1
virtual image, L2 virtual image), the virtual images formed by the
respective lenses can occur at positions which are still closer to
the light emission section. Therefore, the angle of the light
outgoing from the optical lens section can be expanded, and thus,
the uniformity of a larger illumination region can be significantly
improved.
Note that, however, the position of the virtual image I2 formed by
the lens L2 is not necessarily near the light source 1. The virtual
image I2 may be formed at a position which is relatively distant
from the light source. In this case, the lighting device projects
light at a relatively narrow angle. Note that, in a configuration
where light is projected at a relatively narrow angle, placing the
focal point F2 of the second lens L2 at a position which is away
from the L1 virtual image I1 or the light source by a predetermined
distance or more is preferred from the viewpoint of improving the
illuminance uniformity across the illumination region.
FIGS. 27(a) to 27(e) show various positional relationships between
the positions of the focal points F1, F2 of the lenses L1, L2 and
the virtual images I1, I2. In each of the arrangements of FIGS.
27(a) to 27(e), the light source 1 is provided between the first
lens L1 and its focal point F1, and the virtual image I1 of the
light source is formed by the first lens L1. This virtual image I1
is present at an inner position (on the light source side) than the
focal point F2 of the second lens L2. Accordingly, the virtual
image I2 is formed by the second lens L2.
Note that, however, the present inventors found that, when the
virtual image I1 is present near the focal point F2 of the second
lens, there is a probability that the intensity unevenness and
chromaticity unevenness at the emission surface of the surface
light source 1 and the emission surface shape itself are also
reflected in the illumination region on the screen.
FIG. 28 shows the state of the illumination region on the screen in
the case where the virtual image I1 of the light source 1 which is
formed by the first lens L1 is present near the focal point F2 of
the second lens L2 as shown in FIG. 27(a). When the focal point F2
and the virtual image I1 are excessively close to each other, there
is a probability that the intensity unevenness and chromaticity
unevenness produced by a plurality of element LEDs at the emission
surface of the surface light source 1 are more likely to be
perceived also in the illumination region on the screen as if the
virtual image I1 were formed on the screen by the second lens
L2.
To avoid occurrence of such a pseudo image formation and reduce the
probability that the intensity unevenness and chromaticity
unevenness at the emission surface are reflected in the
illumination region, it is preferred that the focal point F2 is
present on the distal side (the side opposite to the light source
side) by a certain distance or more from the virtual image I1.
Further, it is preferred that the focal length of the focal point
F2 of the second lens L2 is not less than a predetermined length.
As will be described later, the position of the focal point F2 of
the second lens L2 may be determined according to, for example, the
size of the surface light source 1. When the surface light source 1
includes a plurality of light-emitting elements, the position of
the focal point F2 of the second lens L2 may be determined
according to, for example, the arrangement pitch of the
light-emitting elements.
FIG. 29 shows a case where the focal point F2 of the second lens L2
is present on the distal side relative to a predetermined reference
position f' (or "reference focal point f'") on the optical axis
(F2<f') and a case where the focal point F2 of the second lens
L2 is present on the proximal side relative to the predetermined
reference position f' (F2.gtoreq.f': including a case where the
focal point F2 is present at the reference position f'). In the
lighting device according to an embodiment of the present
invention, the optical system is designed such that the focal point
F2 is present on the distal side relative to the reference position
f'.
Now, the reference position (or "reference focal point") f' is
described. The reference position f' refers to such a position
that, when the focal point F2 of the second lens is present on the
distal side relative to this position f', the shape of the surface
light source and the intensity unevenness and chromaticity
unevenness are unlikely to be visually perceived in the light
projection region.
When, on the contrary, the focal point F2 is present at the same
position as the reference position f' or at an anterior position
relative to the reference position f', the second lens L2 projects
the virtual image I1, which is approximately in focus, onto an
image surface. As a result, such a phenomenon occurs that the shape
of the emission surface and the intensity unevenness and
chromaticity unevenness at the emission surface are reflected in
the illumination region.
It is inferred that this phenomenon occurs according to a principal
which is similar to that of the phenomenon that the posterior depth
of field is as deep as infinity (which is referred to as
"pan-focus" or "deep focus") when a wide-angle lens (a lens with a
relatively short focal length) is used in a photographic device
such as a camera and the F-number is set to a large value by
controlling the diaphragm.
FIG. 30(a) is a diagram for explaining the aforementioned deep
focus. Here, the thickness of the lens used is neglected, and the
lens has aperture diameter D and focal point f' (F-number is given
by Fno.=f'/D). The distance between an object and the lens is s,
and the distance between the lens and the image surface is s'. In
general, in the case where an image of an object is formed on the
image surface using a lens, the position of the object at which the
image of the object is in focus on the image surface is only one
position. When the object is present anterior or posterior to that
position, the image must be out of focus and blurry. However, in
the case of FIG. 30(a), even when an object on a plane is moved
back and forth within a certain range on the optical axis, it looks
as if it were in focus on the image surface. This is because,
although it is actually out of focus and blurry on the image
surface, the blur cannot be detected if it is smaller than a
certain degree, so that it looks as if it were in focus. Here, in
the case where the size of the permissible limit of the blur is set
as a permissible circle of confusion .epsilon. at the position of
the image surface, a spot of a size which is not more than the
permissible circle of confusion .epsilon. can be regarded as a spot
with no blur.
Also, s'=f's/(f'+s) can be deduced from the Gaussian formula
1/s'-1/s=1/f'. Here, the deep focus is realized under a condition
that it is in focus at the distance from the lens to the object,
s=f'.sup.2/.epsilon.Fno. (hyperfocal distance).
This hyperfocal distance s can be rewritten in regard to the
distance s' between the lens and the image surface into
s'=(D/.epsilon.+D)f'. When this formula holds, the deep focus is
realized. The present inventors found that such deep focus in a
photographic device can also be realized in the lighting device of
the present embodiment.
FIG. 30(b) is a diagram for illustrating a condition under which,
in the lighting device of the present embodiment, an image of the
surface light source is formed in the illumination region with no
blur, as if it were in focus, according to the principle that is
similar to the above-described deep focus (i.e., the shape of the
surface light source and the intensity unevenness and chromaticity
unevenness are reflected in the illumination region).
In the lighting device, the above-described formula
s'=(D/.epsilon.+D)f' can be converted to l'=(D/.epsilon.+D)f' where
l' is the distance from the second lens L2 (when the thickness of
the lens is considered, the principal point on the light source
side) to the virtual image I1. By determining l', D, and .epsilon.
in this formula, the reference focal point f' for the second lens
L2 can be determined.
Here, the effective diameter D is the effective diameter of the
second lens L2. The distance l' from the second lens L2 to the
virtual image I1 can be calculated from the distance from the light
source 1 to the second lens L2 and the distance from the light
source 1 to the virtual image l1. The distance from the light
source 1 to the virtual image I1 can be calculated from the
positional relationship between the light source 1 and the first
lens L1, the refractive index of the first lens L1 and the shape of
the lens surface, etc.
When applied to the lighting device of the present embodiment, the
permissible circle of confusion .epsilon. in the deep focus can be
regarded as a factor which is to be set according to the emission
surface size of the surface light source. When the surface light
source includes a plurality of light-emitting elements which are
arranged with intervals, the permissible circle of confusion
.epsilon. can also be regarded as a factor which is to be set
according to the arrangement pitch of the light-emitting elements
(the pitch of the intensity unevenness and chromaticity
unevenness). When thus applied to the lighting device of the
present embodiment, the permissible circle of confusion .epsilon.
in the deep focus is defined by the size of the emission surface or
the arrangement pitch of the light-emitting elements, and
therefore, these are sometimes referred to as "light source size
factors .epsilon.". As understood from the above-described formula,
the position of the reference focal point f' varies depending on
the setting of the light source size factor .epsilon..
FIG. 31 shows that the position of the reference focal point f'
varies according to the light source size factor .epsilon.. As
illustrated in pattern (A), in the case where the pitch of the LED
chips is considered as the light source size factor .epsilon., the
reference focal point f' as the condition for visually perceiving
the intensity unevenness and chromaticity unevenness on the order
of the pitch on the screen is set to a side which is relatively
close to the light source. As illustrated in pattern (B), in the
case where a size which is greater than the pitch of the LED chips
and which is smaller than the entire size of the light source is
considered as the light source size factor .epsilon., the reference
focal point f' is set to a distal position as compared with the
case of pattern (A). Further, as illustrated in pattern (C), in the
case where the entire size of the light source is considered as the
light source size factor .epsilon., the reference focal point f' is
set to a distal position as compared with the case of pattern
(B).
That is, in the case where the light source size factor .epsilon.
(hereinafter, referred to as "factor .epsilon.") is set to a large
value, the reference focal point f' moves away from the light
source, and the focal point F2 of the second lens L2 is set to a
position which is more distant from the light source than the
reference focal point. Further, as represented by two circles in
the diagram, regions on the emission surface corresponding to the
factor .epsilon. gather in a predetermined region on the
screen.
An image which is formed when the second focal point F2=f' holds in
the above-described configuration is now discussed.
As illustrated in pattern (A), when the factor .epsilon. is smaller
than the intensity unevenness and chromaticity unevenness at the
LED emission surface (the minimum pitch of the arrangement of the
LED elements), an image of the intensity unevenness and
chromaticity unevenness is reflected on the screen. Since regions
enclosed by two circles on the emission surface have different
light emission characteristics, characteristics reaching the two
circles on the screen are different, and it is seen as an image of
the LED chip.
In a preferred example, as illustrated in pattern (B), a plurality
of above-described intensity and chromaticity unevennesses are
present within the range of the factor .epsilon. (not less than the
minimum pitch of the arrangement of the LED elements). In this
case, the light emission characteristics of the regions enclosed by
two circles on the emission surface are averaged, so that an image
of the intensity unevenness and chromaticity unevenness is not
visually perceived on the screen. However, if the size of the LED
emission surface is out of the range of the factor .epsilon., the
difference in intensity and chromaticity between the LED emission
surface and a region outside the LED emission surface (i.e., the
shape of the LED emission surface) is reflected, and sometimes
disadvantageously, an image which has the shape of the LED emission
surface is seen on the screen.
In another preferred example, as illustrated in pattern (C), the
factor .epsilon. is large enough to encompass the entire emission
surface. In this case, the shape of the emission surface is
unlikely to be reflected, so that desirable illumination is
realized on the screen.
Note that, however, the light source size factor .epsilon. may be
set based on another form. An example of setting of the light
source size factor .epsilon. based on another form is described
below.
FIG. 32(a) shows an embodiment where red LEDs, blue LEDs, and green
LEDs are arranged according to a predetermined pattern. In this
case, as shown in the drawing, a plurality of sets of LEDs of three
colors are arranged at the minimum repetition pitch Pa, each of the
LED sets consisting of LEDs of three different colors. In this
case, the repetition pitch minimum Pa is selected as the light
source size factor .epsilon., whereby unevenness across the
illumination region due to the arrangement of respective sets of
LEDs of three colors is prevented from being perceived.
FIG. 32(b) shows a case where the emission surface is formed at
such a pattern that vertically-extending regions of two different
types between which the type, density, and thickness of the
phosphor are different are repeated on a column by column basis.
Although the light-emitting elements may have the same
characteristics, light emitted from the two different type regions
of the emission surface exhibit different wavelength-spectrum
characteristics due to the different phosphor types. In this case,
the repetition pitch minimum Pb of the two-column by two-column
arrangement may be set as the light source size factor .epsilon..
This can prevent occurrence of stripe-pattern unevenness formed due
to the two different type regions which exhibit different
wavelength-spectrum characteristics across the illumination region.
Note that the arrangements of FIGS. 32(a) and 32(b) are merely
exemplary. Even in other arrangements where regions of different
emission intensities and different wavelength-spectrum
characteristics are present in the plane, the minimum repetition
pitch can be used as the light source size factor .epsilon..
As shown in FIGS. 27(a) to 27(e), the angular range of light to be
projected (the extent of the illumination region) varies depending
on the positional relationship between the focal point F2 of the
second lens and the virtual image I1 formed by the first lens L1.
In general, the optical lens is configured such that the light exit
angle is narrowest when the light source is present at the focal
position, and the light exit angle becomes wider as the light
source moves away from the focal position to the lens side. In
other words, the light projection angle becomes narrower as the
focal point F2 of the second lens and the virtual image I1 formed
by the first lens L1 are closer to each other, and the light
projection angle becomes wider as the virtual image I1 is at a more
distant position.
This light projection angle can be represented by the light
spreading angle. Here, the light spreading angle refers to an angle
which is calculated from the width of a region whose illuminance is
not less than 50% in the case where the illuminance achieved at the
center of the illumination region formed on the screen is 100% and
the distance between the light source and the screen. A small light
spreading angle means that the lighting device projects light at a
narrow angle. A large light spreading angle means that the lighting
device projects light at a wide angle.
In the lighting device of the present embodiment, as described
above, the focal point F2 of the second lens is provided at a
distal position relative to the reference position f'. In this
case, a lighting device which projects light with a light spreading
angle of not less than 8.degree., for example, is realized.
In the arrangements shown in FIGS. 27(a) to 27(c), the focal point
F2 of the second lens L2 is present between the virtual image I1
formed by the first lens L1 and the virtual image I2 formed by the
second lens L2. Note that, however, the focal point F2 is present
on the light source side relative to the focal point F1. In these
arrangements also, an illuminance region which has a uniform
illuminance distribution can be formed so long as the focal point
F2 is provided at a distal position relative to the reference
position f'.
On the other hand, as shown in FIGS. 27(d) and 27(e), even when the
focal point F1 is present on the light source side relative to the
focal point F2, an illuminance region which has a uniform
illuminance distribution can be formed. FIG. 27(e) shows the
positional relationship of the focal points f1, f2 (F1, F2) of the
respective lenses, the positions of the respective virtual images
(I1, I2), and the effective focal point f1+f2 (F(1+2)) in the
embodiment shown in FIG. 1. As seen from FIG. 27(e), in the
embodiment shown in FIG. 1, light of a large light spreading angle
can be projected at a wide angle such that the intensity unevenness
and chromaticity unevenness at the emission surface are not
conspicuous.
As described hereinabove, by setting the focal point of the second
lens at a distal position relative to the reference focal point f'
that is determined from the size factor .epsilon. of the emission
surface, the effective diameter D of the second lens, etc.,
illumination with reduced unevenness, i.e., high uniformity, can be
realized.
Note that a mechanism for adjusting the effective aperture D of the
second lens F2 may be provided. In this case, it is preferred that,
for possible arbitrary effective apertures D, the focal length of
the second lens is set such that the shape of the emission surface
and the intensity unevenness and chromaticity unevenness are not
reflected in the illumination region.
Although an optical design consisting of the first lens and the
second lens has been described, the optical system may be
constructed using a larger number of lenses. In this case, assuming
that n lenses are arranged from the light source side, the
above-described first lens may be considered as a lens whose
characteristics are equal to those of the entire lens group
consisting of the first to n-1.sup.th lenses, and the second lens
may be considered as the n.sup.th lens.
(Regarding the Design of the Lens Shape)
The shape of optical lenses included in the optical lens section 2
of the above-described lighting device 11 may be determined
according to the arrangement of focal positions and virtual image
positions in the vicinity of the optical axis. Note that, however,
it is more preferred that the shape of the lenses, including
portions away from the optical axis, is determined according to the
following design criteria.
Specifically, to maximize the utilization efficiency of light
emitted from the light source 1 which has a finite size and secure
the illuminance uniformity across the illumination region, the lens
system is constructed such that the off-axis comatic aberration is
corrected with respect to the size of the surface light source
while the light source 1 is positioned as close as possible to an
optical lens near the light source 1 in order to maintain the
virtual image relationship of generally equal magnification in the
context of the paraxial theory and, meanwhile, an on-axis image
point and an off-axis image point have equal spot shapes and
diameters.
The comatic aberration refers to a phenomenon that light coming out
from one point which is away from the optical axis does not
converge into one point on the image surface but results in an
image which appears to have a tail like a comet. The state of
convergence of light on the image surface is referred to as "spot
shape (spot diagram)".
The aforementioned "axis" refers to the optical axis of a lens. The
term "on-axis" refers to a location on the optical axis of a lens.
The term "off-axis" refers to a location which is away from the
optical axis.
Here, the "virtual image relationship of generally equal
magnification in the context of the paraxial theory" refers to a
condition under which the size of the L1 virtual image and the L2
virtual image in FIG. 4(a) is equal to or several times greater
than the light source and meanwhile the L1 virtual image and the L2
virtual image occur near the light source.
Further, correcting "the off-axis comatic aberration" means
changing the shape of a lens portion away from the optical axis
such that light coming out from a location which is away from the
optical axis converges into one point on the image surface.
Further, "an on-axis image point and an off-axis image point have
equal spot shapes and diameters" means changing the shape of a lens
portion away from the optical axis such that the spot on the image
surface of light coming out from a location on the optical axis and
the spot on the image surface of light coming out from a location
away from the optical axis have generally equal shapes and
areas.
Effects of Present Embodiment
FIG. 6 Through FIG. 11
Details of the effects in the lighting device 11 that has the
above-described configuration are described below with reference to
FIG. 6 through FIG. 11.
As shown in FIG. 6, in the case where the evaluation plane is 1 m
distant from the lighting device 11 such as shown in FIG. 2, the
resultant illuminance distribution across the evaluation plane is
as shown in FIG. 7. In FIG. 7, the in-plane distribution is
monochromatically shown according to the illuminance intensity. A
black portion represents the minimum illuminance, and a white
portion represents the maximum illuminance.
The cross-sectional profile of the illuminance distribution at the
central portion was checked as shown in FIG. 7, and as a result, it
was confirmed that generally uniform illuminance was achieved
across the illumination region as shown in FIG. 8.
The lighting device of the present embodiment is capable of
uniformly illuminating a predetermined illumination region not only
when all regions of the emission surface of the light source 1
uniformly emit light but also when, for example, a plurality of
minute emission surfaces are arranged over the emission surface of
the light source 1 as shown in FIG. 9(a). For example, it is
possible that a plurality of LED emitters are arranged over the
emission surface of the light source 1.
As shown in FIG. 9(b), even when some of the plurality of minute
emission surfaces arranged over the emission surface of the light
source 1 emit smaller amounts of light, it is possible to uniformly
illuminate a predetermined illumination region. This is because, as
in the case that has been illustrated with reference to FIG. 5(a),
even light coming from a location on the emission surface of the
light source 1 which is away from the optical axis can illuminate
the same illumination region as that illuminated by light coming
from a location on the optical axis. That is, no matter which
portion of the emission surface light comes from, the light can
illuminate the same illumination region. Therefore, even when some
portions of the emission surface emit smaller amounts of light, it
would not affect the uniformity of illumination across the
illumination region.
FIG. 9(c) shows the illuminance distribution produced by the
emission surface of the light source 1 shown in FIG. 9(b). As also
seen from this illuminance distribution, it would not affect the
uniformity of illumination across the illumination region.
As shown in FIGS. 32(a) and 32(b), the plurality of minute emission
surfaces of FIG. 9(a) may emit light of different dominant
wavelengths. Alternatively, a plurality of light-emitting
substances which emit light of different dominant wavelengths may
be combined. In that case, light of different colors generally
uniformly illuminate the same illumination region, and therefore, a
lighting device which has wide color reproducibility can be
realized.
By thus combining a plurality of light-emitting substances which
emit light of different dominant wavelengths, colors from a wide
range over the chromaticity coordinates can be reproduced.
Due to various variations in the manufacturing process of the light
emitters, the LED light source have large variations in the
emission characteristics, such as the amount of emission, the
dominant wavelength of emission, the emission wavelength band, etc.
In the existing procedures, in the case where the LED light source
is used, light emitters which have similar emission characteristics
are selected for use, and this selection process is a factor which
increases the cost.
Assuming that one of the emission surfaces of the light source 1
shown in FIG. 9(a) is realized by one LED light source, even if the
LED light sources that constitute the emission surface have varying
emission characteristics as shown in FIG. 9(b), it would not affect
the uniformity of illumination across the illumination region as
shown in FIG. 9(c). Therefore, the variations of the LED light
sources can be averaged within the illumination region. Thus,
selection of the LED light sources is not necessary, and cost
reduction can be realized.
As seen from these results, a plurality of light-emitting
substances can be arranged, and therefore, even if one of the
light-emitting substances is inoperative due to breakdown, the
uniformity of the illumination region would not vary. Thus, it is
not necessary to replace the entire lighting device, and extension
of the life duration of the lighting device can be expected.
The cross-sectional illuminance distributions at places which are 1
m and 5 m distant from the lighting device 11 as shown in FIG. 10
are as shown in FIGS. 11(a) and 11(b).
FIG. 11(a) shows the cross-sectional illuminance distribution at a
place which is 1 m distant from the lighting device 11. FIG. 11(b)
shows the cross-sectional illuminance distribution at a place which
is 5 m distant from the lighting device 11.
Although not shown in the drawings, even cross-sectional
illuminance distributions at the places which are 2 m and 3 m
distant, or distant by any other arbitrary distance, from the
lighting device 11 are also uniform illuminance distributions as in
FIGS. 11(a) and 11(b).
As seen from the foregoing, the cross-sectional illuminance
distribution of light emitted from the lighting device 11 has
uniform illuminance distribution at any position so long as it is
distant by a certain distance or more. Here, the "certain distance
or more" means an extent which is not less than twice the maximum
diameter of the optical lenses L1, L2 that are constituents of the
optical lens section 2 of the lighting device 11.
EXAMPLES
FIG. 12, FIG. 13
Now, a prototype example of the lighting device 11 of FIG. 1 is
shown in FIG. 12(a).
The light source 1 used was a white LED package of about 6
mm.times.6 mm.
The first optical lens L1 of the optical lens section 2 was made of
polycarbonate which had refractive index nd=about 1.585. The radius
of curvature of the light entry surface provided on the light
source side was 9.2 mm. The radius of curvature of the light exit
surface was 6.0 mm. The lens outside diameter was 12 mm. The lens
thickness was 5 mm.
The second optical lens L2 used was made of PMMA which had
refractive index nd=about 1.49. The light entry surface was a flat
surface. The radius of curvature of the light exit surface was
20.966 mm. The conic constant was 0.28119. The aspheric
coefficients of high orders, 4.sup.th order, 6.sup.th order,
8.sup.th order, 10.sup.th order, and 12.sup.th order, were
-5.2.times.10.sup.-7, -1.8914.times.10.sup.-8,
3.4858.times.10.sup.-10, -9.7419=10.sup.-13, and
2.6235.times.10.sup.-16, respectively. The lens outside diameter
was 35 mm. The lens thickness was 10.5 mm.
The white LED package, the first optical lens L1, and the second
optical lens L2 were arranged such that the centers of these
elements were on the optical axis. Meanwhile, the distance along
the optical axis between the emission surface of the white LED
package and the light entry surface of the first optical lens L1
was 1.5 mm. The distance along the optical axis between the light
exit surface of the first optical lens L1 and the light entry
surface of the second optical lens L2 was 2.0 mm.
In that case, the focal lengths of the optical lenses L2, L1 were
18.52 mm and 42.47 mm, respectively, and the effective focal length
of the optical lenses L2, L1 was 14.12 mm. In a scale where the
emission surface of the light source section was at 0 (origin) and
the direction of exit of light was the positive (+) direction, the
focal positions f1, f2 of the optical lenses L1, L2 and the
effective focal position f1+f2 were -11.30 mm, -26.94 mm, and -5.14
mm, respectively.
On the other hand, the positions of virtual images formed by the
optical lenses L1, L2 (L1 virtual image, L2 virtual image) were
deduced by calculation, and as a result, the position of the L1
virtual image was -1.61 mm, and the position of the L2 virtual
image was -9.74 mm.
Thus, it was confirmed that, in the lighting device 11 that had the
above-described configuration, the focal points f1, f2 of the
optical lenses L1, L2 that were constituents of the optical lens
section 2 were present on a side opposite to surfaces of
corresponding virtual images (L1 virtual image, L2 virtual image)
facing on the light source 1 relative to the respective virtual
images formed by the optical lenses L1, L2 (L1 virtual image, L2
virtual image), i.e., the lighting device 11 was designed as shown
in FIG. 1.
An illuminance experiment for the lighting device 11 that has the
above-described configuration was carried out.
The result of this experiment is shown in FIG. 12(b). It was found
from FIG. 12(b) that a predetermined illumination region was
illuminated with uniform illuminance.
A prototype example of the lighting device 11 of FIG. 2 is shown in
FIG. 13(a).
The light source 1 used was a white LED package with a diameter of
2 mm.
The first optical lens L1 of the optical lens section 2 was made of
glass material SLAH53 which had refractive index nd=about 1.806.
The radius of curvature of the light entry surface provided on the
light source side was 2.96 mm. The radius of curvature of the light
exit surface was 2.69 mm. The lens outside diameter was 5 mm. The
lens thickness was 1.6 mm.
The second optical lens L2 used was made of PMMA which had
refractive index nd=about 1.49. The radius of curvature of the
light entry surface provided on the light source side was 65.4 mm.
The conic constant of the light entry surface was -5.0. The
aspheric coefficients of high orders, 4.sup.th order, 6.sup.th
order, and 8.sup.th order, were -5.97.times.10.sup.-5,
-7.927.times.10.sup.-6, and -7.278.times.10.sup.-7, respectively.
The radius of curvature of the light exit surface was 8.0 mm. The
conic constant of the light exit surface was 0.73. The aspheric
coefficients of high orders, 4.sup.th order, 6.sup.th order,
8.sup.th order, 10.sup.th order, and 12.sup.th order, were
1.225.times.10.sup.-4, -3.777.times.10.sup.-6,
1.054.times.10.sup.-7, -1.83.times.10.sup.-9, and
4.2397.times.10.sup.-11, respectively. The lens outside diameter
was 10 mm. The lens thickness was 3.0 mm.
The white LED package, the first optical lens L1, and the second
optical lens L2 were arranged such that the centers of these
elements were on the optical axis. Meanwhile, the distance along
the optical axis between the emission surface of the white LED
package and the light entry surface of the first optical lens L1
was 0.5 mm. The distance along the optical axis between the light
exit surface of the first optical lens L1 and the light entry
surface of the second optical lens L2 was 0.1 mm.
In that case, the focal lengths of the optical lenses L2, L1 were
9.899 mm and 14.69 mm, respectively, and the effective focal length
of the optical lenses L2, L1 was 5.81 mm. In a scale where the
emission surface of the light source section was at 0 (origin) and
the direction of exit of light was the positive (+) direction, the
focal positions f1, f2 of the optical lenses L1, L2 and the
effective focal position f1+f2 were -6.76 mm, -10.68 mm, and -2.85
mm, respectively.
On the other hand, the positions of virtual images formed by the
optical lenses L1, L2 (L1 virtual image, L2 virtual image) were
deduced by calculation, and as a result, the position of the L1
virtual image was -0.10 mm, and the position of the L2 virtual
image was -0.75 mm.
Thus, it was confirmed that, in the lighting device that had the
above-described configuration, the focal points f1, f2 of the
optical lenses L1, L2 and the effective focal position f1+f2 were
present on a side opposite to surfaces of all the virtual images
(L1 virtual image, L2 virtual image) facing on the light source 1
relative to the respective virtual images formed by the optical
lenses L1, L2 (L1 virtual image, L2 virtual image), i.e., the
lighting device 11 was designed as shown in FIG. 2.
An illuminance experiment was carried out using the lighting device
11 that has the above-described configuration. The result of the
illuminance experiment is shown in FIG. 13(b). As seen from FIG.
13(b), the lighting device 11 is capable of illuminating a
predetermined illumination region with uniform illuminance.
Embodiment 2
Another embodiment of the present invention will be described
below. Note that, for the sake of convenience of description,
components which have identical functions as those of Embodiment 1
are designated by the same reference numerals, and detail
description thereof is herein omitted.
(Configuration of Lighting Device) . . . FIGS. 14 and 15
FIG. 14 is a diagram showing a general configuration of a lighting
device 12 according to the present embodiment.
FIG. 15 is an enlarged view of the major portion A shown in FIG.
14.
The lighting device 12 has a configuration where optical lenses 3,
4 are further added on the light exit side of the optical lens
section 2 of Embodiment 1 as shown in FIG. 14.
That is, where the above-described optical lens section 2 is
referred to as the first optical lens section, the lighting device
12 has a configuration in which the second optical lens section
formed by at least two optical lenses (optical lenses 3, 4) is
provided on the light exit side of the first optical lens
section.
The optical lens 3 is a concave lens. The optical lens 3 is closest
to the optical lens section 2 and is arranged such that the concave
surface side faces on the optical lens section 2.
The optical lens 4 is a convex lens. The optical lens 4 is more
distant from the optical lens section 2 than the optical lens
3.
By thus further providing the optical lenses 3, 4 on the outer side
of the optical lens section 2, the light exit angle of light
emitted from the lighting device 12 can be narrowed as shown in
FIG. 15.
Effects of Present Embodiment
FIG. 16 Through FIG. 19
In the lighting device 12 that has the above-described
configuration, the lens shape of the added optical lenses 3, is
optimized, whereby the illumination region can be uniformly
illuminated as shown in FIG. 16.
In this case, to achieve both narrowing of the light exit angle and
uniformity of the illumination region, it is more preferred to use
a concave lens and a convex lens in combination as described above.
This is because using the concave lens and the convex lens in
combination enables mutual correction of aberrations occurring in
the respective lenses and achievement of uniformity of the
illumination region.
The arrangement of the added lenses is not limited to the
arrangement positions of FIG. 14. The added lenses may be arranged
at other positions.
FIG. 17 is a diagram showing a general configuration of the
lighting device 12 in which the optical lenses 3, 4 are placed at
different positions from those of the optical lenses 3, 4 shown in
FIG. 14.
FIG. 18 is an enlarged view of the major portion B shown in FIG.
17.
As shown in FIG. 17, part of the optical lenses 3, 4 added in FIG.
14 is placed at a different position, whereby the angular
distribution of light emitted from the lighting device 12 can be
changed.
Note that even when the angular distribution is changed, the
illumination region can be generally uniformly illuminated as shown
in FIG. 19.
As described above, by further adding the optical lenses 3, 4 on
the light exit side in the lighting device 11 that has been
described in Embodiment 1, the light exit angle can be narrowed.
Further, by changing the arrangement of the added optical lenses,
the light exit angle can also be adjusted (controlled).
Even when the optical lenses 3, 4 are added to control the light
exit angle as described hereinabove, the illuminance uniformity
across the illumination region can be maintained in each case as
shown in FIG. 16 and FIG. 19.
Note that the second optical lens section is not limited to the
optical lenses 3, 4 shown in FIG. 14. For example, a plurality of
optical lenses which are combined so as to have the same optical
characteristics as those of the optical lens 3 may be used in place
of the optical lens 3. The number of optical lenses included in the
second optical lens section is not particularly limited.
As the number of optical lenses increases, improvement of the
in-plane uniformity and control of the light projection angle are
achieved more easily. On the other hand, however, it is necessary
to consider various disadvantages, such as decrease of the light
transmittance due to an increased number of lens interfaces, and
increase of cost due to an increased number of lenses.
Embodiment 3
Still another embodiment of the present invention will be described
below. Note that, for the sake of convenience of description,
components which have identical functions as those of Embodiments 1
and 2 are designated by the same reference numerals, and detail
description thereof is herein omitted. In an example described in
this section, two optical lenses of the optical lens section 2 are
integrated together.
(Configuration of Lighting Device) . . . FIGS. 20 and 21
FIG. 20 is a diagram showing a general configuration of a lighting
device 13a according to the present embodiment.
FIG. 21 is a diagram showing a general configuration of a lighting
device 13b according to the present embodiment.
The lighting device 13a shown in FIG. 20 is an example where the
optical lenses L1, L2 are integrally molded to form an optical lens
section 22.
Specifically, the optical lenses L1, L2 are integrally molded with
a die using a resin such as an acrylic material to form the optical
lens section 22.
On the other hand, the lighting device 13b shown in FIG. 21 is an
example where the optical lenses L1, L2 are adhered together to
form an optical lens section 23.
Specifically, a lens which is close to the emission surface of the
light source 1 (optical lens L1) and a lens which is distant from
the emission surface of the light source 1 (optical lens L2) are
separately molded, and then, the lenses are adhered together at
about the centers of the lenses to form the optical lens section
23.
The optical lens shapes are now compared between the optical lens
section 2 illustrated in Embodiment 1 (FIG. 1) and the optical lens
section 22 shown in FIG. 20. In either case, light emitted at a
wide angle from the light source 1 greatly changes its traveling
direction due to refraction at the same four air interfaces.
On the other hand, light emitted in a direction perpendicular to
the light source in FIG. 1 is generally perpendicularly incident
upon the respective air interfaces of the optical lens section 2.
Therefore, even when portions at about the center of the optical
lens section 22 are in contact with each other or joined together
as shown in FIG. 20, uniformity of the illumination region is
realized while the light exit angle distribution is not largely
affected.
Effects of Present Embodiment
FIGS. 22 and 23
In the lighting device 13a that includes the optical lens section
22 in which the optical lens is integrally molded as shown in FIG.
20, when the evaluation plane is placed at a position which is 1 m
distant from the lighting device 13a so as to be parallel to the
emission surface as shown in FIG. 22, the illuminance distribution
across the illumination region is generally uniform as shown in
FIG. 23.
Thus, the merit of adhering together two lenses that are
constituents of an optical lens lies in cost reduction due to
simplified alignment of the emission surface and the optical lens.
Also, the procedure of fixing the emission surface and the optical
lens during use can be simplified.
Further, the merit of integrally molding an optical lens includes
not only cost reduction due to the aforementioned simplified
alignment and fixing procedure but also cost reduction due to
decrease of the molding cycles from two cycles to one cycle. Also,
the process of adhering two lenses together can be omitted, and
this contributes to cost reduction.
<Variation> . . . FIGS. 24 and 25
FIG. 24 shows a case where a hexagonal opening (aperture) section 5
is provided on the light exit side of the above-described lighting
device 11 of Embodiment 1. Only part of light emitted from the
above-described lighting device 11 traveling toward the hexagonal
opening section 5 passes through the hexagonal opening section 5
while the remaining part of the light is reflected or absorbed.
FIG. 25 shows a two-dimensional illuminance distribution achieved
in a case where the evaluation plane is 1 m distant from the
lighting device 11. In this case, it is possible to illuminate the
evaluation plane such that the illumination region has a shape
approximately equal to that of the opening section 5 and the
illuminance across the illumination region is uniform. Further,
even when the evaluation plane is distant from the surface light
source or the lighting device, illumination is also achieved while
the shape and uniformity of the illumination region are
maintained.
<Supplementary Explanation> . . . FIG. 26
(1) The limit of the arrangement range of the light source 1 is
explained with reference to FIG. 26.
The arrangement range of the above-described light source 1 is
preferably limited within a range which satisfies the following
formula: h.ltoreq.2 (d(2R-d))
Here, h is the width of the arrangement range of the light emission
section, d is the distance from the light source to the optical
lens L1 interface on the optical axis, and R is the radius of
curvature of the inner lens of the optical lens L1.
By arranging the light source 1 within the above-described range,
all of the light emitted from the light source 1 can be brought
into the optical lens L1 that is the first lens, so that the light
utilization efficiency can be improved.
(2) The relationship between the focal position and virtual image
position of the optical lens section 2 and the position of the
light source is explained.
As in the above-described configuration, the focal position of the
optical lens section 2 that is provided on the light exit surface
side of the light source 1 is placed at a distant position behind
the positions of the L1 virtual image and the L2 virtual image
formed by the optical lenses L1, L2 (in a direction opposite to the
light exit side of the lens), whereby the positions of the light
source 1 and the virtual images (L1 virtual image, L2 virtual
image) are moved relatively close to the optical lens section
2.
In this case, the following formula holds: 1/a-1/b=1/f (1) where f
is the distance from the lens principal point to the focal position
of the optical lens section 2, a is the distance from the lens
principal point to the light source, and b is the distance from the
lens principal point to the virtual image. Here, the lens principal
point refers to a position of a thin lens in the case where the
lens is replaced by the thin lens whose lens thickness is
negligible, in which only behaviors of a light ray coming into the
lens and a light ray outgoing from the lens are represented.
In the lighting device 11 that has the above-described
configuration, the virtual image positions are relatively close to
the optical lens section 2 as compared with the focal positions f1,
f2 of the optical lenses L1, L2. Therefore, the following formula
holds: f>b (2)
Here, the following formula is deduced from formula (1) shown
above: 1/a=1/b+1/f=(b+f)/bf (3)
Formula (3) can be further developed into the following formula:
a=bf/(b+f)=f/(1+f/b) (4)
Here, the following formula is deduced from formula (2): f/b>1
(5)
Therefore, assigning formula (5) to formula (4) leads to the
following formula: a<f/2
That is, by making the distance a from the lens principal point to
the light source shorter than a half of the distance f from the
lens principal point to the focal position, the virtual image
position can always be relatively close to the optical lens as
compared with the focal position of the optical lens.
(3) Since part of the light is reflected at the lens interfaces of
the optical lens section 2, it is more preferred that the lens
surface of each optical lens is provided with a surface treatment
for antireflection purposes. A common example of the surface
treatment for antireflection purposes is an antireflection film
consisting of a plurality of thin films which have different
refractive indices for reducing the surface reflection. Another
example is to form a minute uneven shape of not more than one
micrometer (moth-eye structure) over the lens surface of each
optical lens for reducing the interface reflection.
The method of reducing the interface reflection at the lens surface
of each optical lens is not limited to the above-described
example.
(4) The emission wavelength of the light source section is not
limited to visible light. A light-emitting element which is capable
of emitting at ultraviolet or infrared wavelengths may be used.
(5) In the embodiment described hereinabove, the shape of each lens
is a shape of rotational symmetry, although the present invention
is not limited to this example. It may be a lenticular shape evenly
extending in the depth direction of the drawing. In this case, the
effects are achieved only in a direction parallel to the lens
cross-sectional direction of the lenticular-shaped lens. For
example, this is suitable to a case where a cold cathode tube or
LED lamps which are arranged in series are used as the light
source. Combining a stick-shaped light source section and a
lenticular-shaped optical lens enables the uniform illumination
region to have a rounded rectangular shape.
[Lighting Device to Form Non-Circular Illumination Region
(Embodiments 4-1 Through 4-7)]
Hereinafter, lighting devices configured to form a non-circular
illumination region using an optical lens which includes a
plurality of unit faces over a lens surface will be described.
Embodiment 4-1
FIGS. 33(a) and 33(b) are a perspective view and cross-sectional
view showing a lighting device 100 of Embodiment 4-1. FIG. 33(c) is
a perspective view showing the shape of the light exit side surface
of a second lens L2.
As shown in FIG. 33(b), the lighting device 100 includes a surface
light source 1, a first lens L1 provided on the light exit side of
the surface light source 1, and a second lens L2 provided on the
light exit side of the first lens L1. The center of the surface
light source 1 and the lens surface centers of the lenses L1, L2
are aligned on one straight line (optical axis). The distance
between the light exit surface of the surface light source 1 and
the principal point of the first lens L1 is, for example, not less
than the depth of the cavity of a concaved light entry surface of
the first lens L1 and not more than the thickness of the first lens
L1. The distance between the principal point of the first lens L1
and the principal point of the second lens L2 is, for example, not
less than the distance between the principal points in the case
where the first lens L1 and the second lens L2 are in contact with
each other and not more than the distance of D/(2tan(.alpha.))
where .alpha. is the angle of a light ray outgoing from the first
lens L1 and D is the aperture diameter of the second lens L2.
Note that the optical system provided in the lighting device 100
may be configured to further include other optical elements than
the first lens L1 and the second lens L2. Hereinafter, however, the
configuration of the surface light source 1, the first lens L1, and
the second lens L2 is described.
The surface light source 1 may be configured to include a plurality
of light-emitting elements (e.g., a plurality of LEDs) arranged
over the emission surface as in the above-described embodiments. In
this case, the planar shape of the emission surface of the surface
light source 1 may be defined by the perimeter shape of a region in
which the plurality of light-emitting elements are arranged. For
example, it is a quadrangular shape, although the present invention
is not limited to this example. It may be a circular shape. The
size of the emission surface of the surface light source 1 is, for
example, set with the effective diameter of the concaved light
entry surface of the first lens L1 being the maximum.
In the present embodiment, the first lens L1 is a convex meniscus
lens which is provided so as to cover the entirety of the surface
light source 1. The light entry surface of the first lens L1 is
formed by a concave curved surface, and the light exit surface is
formed by a convex curved surface. These light entry surface and
light exit surface may be any of a spherical surface, an aspherical
surface, and a free curved surface.
The second lens L2 generally has the shape of a plano-convex lens.
The light entry surface of the second lens L2 is a flat surface.
The light exit surface S0 of the second lens L2 generally has a
convex surface shape. Note that, however, in the present
embodiment, the light exit surface S0 of the second lens L2 is
configured to include a non-revolution surface as the lens
surface.
The term "non-revolution surface" used in this specification is now
described. In this specification, the "non-revolution surface"
means any curved surface which is not a "revolution surface". The
"revolution surface" means a surface of a solid of revolution that
is formed by rotating a line segment (straight line or curve) which
serves as a generatrix around a rotation axis. In general, a
surface of a lens included in an optical system is configured to
form a revolution surface around the optical axis as the rotation
axis. Such a revolution surface (lens surface) is sometimes called
"axisymmetric revolution surface".
The "revolution surface" always forms a line segment (generatrix)
of the same shape in an arbitrary cross section including the
rotation axis. On the other hand, the "non-revolution surface"
forms, in some cases, line segments of different shapes in
different cross sections including the rotation axis.
In this specification, the terms "body of rotational symmetry" and
"property of rotational symmetry" are also used. The "body of
rotational symmetry" means a body which is rotationally symmetrical
about a predetermined axis. For example, a cube is a body of
rotational symmetry which is 4-fold symmetrical about an axis
extending through a face center. A surface of a "body of rotational
symmetry" has a "property of rotational symmetry" about the
aforementioned predetermined axis.
In various embodiments which will be described later, for example,
a lens used for formation of a square illumination region has a
"non-revolution surface" at its lens surface and, meanwhile, has a
"property of rotational symmetry" of 4-fold symmetry about the
optical axis. Also, for example, a lens used for formation of an
equilateral triangular illumination region has a "non-revolution
surface" at its lens surface and, meanwhile, has a "property of
rotational symmetry" of 3-fold symmetry about the optical axis.
Again, the second lens L2 of the present embodiment is described.
The second lens L2 is a body of 4-fold rotational symmetry about an
axis extending through the center O of the lens surface and
perpendicular to the lens surface (typically, identical with the
optical axis). In this configuration, the light exit surface S0 of
the second lens L2 has four unit faces S1 to S4. The four unit
faces S1 to S4 are separated by four boundary lines B1 to B4
extending outward from the center O of the lens surface which is
placed on the optical axis. In the lighting device 100 of the
present embodiment, an illumination region which has a generally
square shape is realized by using a lens in which a non-revolution
surface including such four unit faces S1 to S4 is formed.
Note that light which has passed through the first lens L1 is
incident upon a region within a predetermined range extending from
the lens surface center O of the second lens L2 and, typically, not
incident upon a portion near the perimeter of the lens surface S0.
Therefore, in the present embodiment, the perimeter shape of the
lens surface S0 is not particularly limited and is not necessarily
limited to a quadrangular shape.
Each of the four unit faces S1 to S4 is a free curved surface. Each
free curved surface has different curvatures in the x-direction and
the y-direction (which are orthogonal to each other) shown in FIGS.
33(a) and 33(c). The four unit faces S1 to S4 are symmetrically
arranged about an axis extending through the center O of the lens
surface and parallel to the z-direction (a direction orthogonal to
the x-direction and the y-direction). The four unit faces S1 to S4
have substantially equal curvature distributions.
The boundary lines B1 to B4 provided between the above-described
four unit faces S1 to S4 correspond to portions at which the
curvature varies discontinuously. A known example of the lens that
have boundary lines at which the curvature varies discontinuously
is a Fresnel lens which has concentric boundary lines. However, the
boundary lines B1 to B4 formed in the lenses of the lighting
devices of the embodiments of the present invention are of a
different type from the boundary lines formed on the surface of the
Fresnel lens, i.e., are not concentrically arranged boundary
lines.
Next, the unit faces S1 to S4 are described more specifically.
Hereinafter, the unit face S1, which is one of the four unit faces
shown in FIG. 33(c), is only described although the same
description applies to the other unit faces S2 to S4.
On the unit face S1, there are three points P1, P2, P3 which are
aligned in the y-direction shown in FIG. 33(c). The unit face S1 is
formed so as to satisfy the following formula:
Rx1.noteq.Rx2.noteq.Rx3 where Rx1, Rx2, Rx3 are the radii of
curvature in the x-direction at the points P1, P2, P3,
respectively.
Note that, in the embodiment shown in the drawing, the curved
surface is determined so as to satisfy the relationship of
Rx1>Rx2>Rx3, although this relationship is merely exemplary.
The present invention is not limited to this example. In some
cases, the curved surface may satisfy the relationship of
Rx1<Rx2<Rx3.
Also, the three points P1, P2, P3 are present on a curve which has
an equal curvature in the y-direction. At the respective points,
the curvatures in the y-direction are equal to one another.
On the other hand, as shown in FIG. 33(c), on the unit face S1,
there are three points Q1, Q2, Q3 which are aligned in the
x-direction. The unit face S1 is formed so as to satisfy the
following formula: Ry1.noteq.Ry2.noteq.Ry3 where Ry1, Ry2, Ry3 are
the radii of curvature in the y-direction at the three points Q1,
Q2, Q3, respectively.
In the embodiment shown in the drawing, the curved surface is
determined so as to satisfy the relationship of Ry1>Ry2>Ry3,
although this relationship is merely exemplary. The present
invention is not limited to this example. In some cases, the curved
surface may satisfy the relationship of Ry1<Ry2<Ry3.
Also, the three points Q1, Q2, Q3 are present on a curve which has
an equal curvature in the x-direction. At the respective points,
the curvatures in the x-direction are equal to one another.
That is, each of thick lines extending in the y-direction shown in
the drawing (e.g., curves extending through P1, P2, P3) is the set
of points which have different curvatures in the x-direction and
have equal curvatures in the y-direction. Each of thick lines
extending in the x-direction shown in the drawing (e.g., curves
extending through Q1, Q2, Q3) is the set of points which have
different curvatures in the y-direction and have equal curvatures
in the x-direction.
Next, a specific design of the above-described lens surface is
described.
Table 1 presented below shows the height in the z-direction at the
respective x, y coordinates (the lens thickness at the respective
points) over the unit face S1 in the x-y plane including the
x-direction and the y-direction in FIG. 33(c) (a plane orthogonal
to the optical axis). The lens height at the respective x, y
coordinates, z=f(x, y), is defined by, for example, the following
formula:
f(x,y)=-c.sub.yx.sup.2/(1+(1-(1+k)c.sub.y.sup.2x.sup.2).sup.1/2)-c.sub.xy-
.sup.2/(1+(1-c.sub.x.sup.2y.sup.2).sup.1/2)
Here, c.sub.y is 1/Ry, c.sub.x is 1/Rx, and k is the conic constant
(shown as "Conic Cy" in Table 1). The lens height z is a value that
is obtained relative to the height at the lens center O which is
zero (0).
TABLE-US-00001 TABLE 1 Radius of Curvature Rx 54 53.4 52.8 52.2
51.6 51 50.4 49.8 49.2 48.6 48 Radius of x Curvature Ry Conic Cy y
-17.5 -15.8 -1.4 -12.3 -10.5 -8.75 -7 -5.25 -3.5 -17.5 0 53.992 1.5
-17.5 -5.97 48.52 1.5 -15.75 -5.81 -5.13 43.732 1.5 -1.4 -5.79
-4.98 -4.3 39.628 1.5 -12.25 -5.91 -4.94 -4.14 -3.48 36.208 1.5
-10.5 -6.17 -5.01 -4.08 -3.31 -2.69 33.472 1.5 -8.75 -6.57 -5.16
-4.08 -3.21 -2.51 -1.95 31.42 1.5 -7 -7.07 -5.37 -4.11 -3.14 -2.37
-1.77 -1.29 30.052 1.5 -5.25 -7.59 -5.55 -4.15 -3.09 -2.27 -1.62
-1.12 -0.75 29.020 1.5 -3.5 -8.22 -5.70 -4.22 -3.08 -2.21 -1.52 -1
-0.61 -0.34 28.342 1.5 -1.75 -8.91 -5.95 -4.29 -3.09 -2.18 -1.47
-0.93 -0.53 -0.25 -0.- 09 28 1.5 0 -9.49 -6.08 -4.34 -3.11 -2.18
-1.46 -0.91 -0.5 -0.22 -0.05 0 28.342 1.5 1.75 -8.91 -5.95 -4.29
-3.09 -2.18 -1.47 -0.93 -0.53 -0.25 -0.0- 9 29.026 1.5 8.5 -8.22
-5.76 -4.22 -3.08 -2.21 -1.52 -1 -0.61 -0.34 30.052 1.5 5.25 -7.59
-5.55 -4.15 -3.09 -2.27 -1.62 -1.12 -0.75 31.42 1.5 7 -7.07 -5.37
-4.11 -3.14 -2.37 -1.77 -1.29 33.472 1.5 8.75 -6.57 -5.16 -4.08
-3.21 -2.51 -1.95 36.208 1.5 10.5 -6.17 -5.01 -4.08 -3.31 -2.69
39.628 1.5 12.25 -5.91 -4.94 -4.14 -3.48 43.732 1.5 1.4 -5.79 -4.98
-4.3 48.52 1.5 15.75 -5.81 -5.13 53.992 1.5 17.5 -5.97
Note that the lens design which has been described above is merely
exemplary. As a matter of course, the free curved surface may be
defined using a different formula. For example, each of the unit
faces S1 to S4 may be a free curved surface whose curvatures in the
x-direction and the y-direction are determined using an aspheric
formula including an aspheric function which includes terms of
higher orders and aspheric coefficients of high orders
corresponding to those terms.
The shape of the free curved surface may be appropriately
determined according to the shape of a desired illumination region.
For example, by setting the above-described radii of curvature Rx
and Ry to relatively small values (i.e., by setting the curvatures
to large values), the vertical and horizontal dimensions of the
illumination region can be made relatively small.
In the lighting device 100 that has the above-described
configuration, light emitted from the surface light source 1 is
converged by the first lens L1 that is a convex meniscus lens and
then refracted by the second lens L2 that includes the four unit
faces S1 to S4 over the lens surface, whereby the light is incident
upon a generally square region on the screen.
As shown in FIGS. 27(b) to 27(f), by designing the optical system
such that the focal point F2 of the second lens L2 is placed at a
position which is more distant than the virtual image I1 formed by
the first lens L1 and which is more distant than the reference
focal point f', a homogeneous illumination region can be realized
in which the illuminance unevenness is not conspicuous.
FIG. 34(a) shows the illuminance distribution across a region
illuminated by the lighting device 100. FIGS. 34(b) and 34(c) show
a planar shape of the illumination region (spot shape LS). Note
that FIG. 34(b) shows a spot shape obtained from the design values
of the optical system. FIG. 34(c) shows a spot shape obtained using
an actually manufactured optical system.
As shown in the drawings, by providing a lens surface of a
non-revolution surface consisting of the above-described four free
curved surfaces at the light exit surface S0 of the second lens L2,
a generally square spot shape LS can be realized. In the present
embodiment, light from the light source is refracted by the lens
surface such that the light is converged into a quadrangular shape
without blocking part of the light from the light source by a light
blocking member or the like, the light utilization efficiency can
be improved.
As a result of a calculation by simulation, it was confirmed that
according to the lighting device 100 of the present embodiment the
light utilization efficiency of the light reaching an illumination
region which is 1 m ahead is about 80%. Here, the light utilization
efficiency means the ratio of the amount of light reaching a
surface to be illuminated which is 1 m ahead after passage through
the lens to the amount of light emitted from the light source
section to the air. The lighting device 100 of the present
embodiment includes the light source section and two lenses, i.e.,
the minimum necessary basic elements, and none of the basic
elements absorbs or blocks light. It is therefore inferred that
such a high light utilization efficiency was achieved.
As seen from FIG. 34(a), using the lighting device 100 of the
present embodiment enables improvement of the illuminance
uniformity. Therefore, it is suitably used as a spotlight of a
different shape which is capable of illuminating with uniform
illuminance.
The first lens L1 or the second lens L2 is made of, for example, a
resin material although the present invention is not limited to
this example. It is desired that the first lens L1 or the second
lens L2 is a transparent refractive index medium which transmits
visible light. For some uses, a refractive index medium which
transmits ultraviolet or infrared ranges can also be used. Typical
examples of the lens material include resins such as PMMA
(polymethyl methacrylate resin), PC (polycarbonate), PS
(polystyrene), COP (cycloolefin polymer) and silicone, and
inorganic materials such as glass. The refractive index of the
first lens L1 or the second lens L2 is set to, for example, 1.3 to
2.0.
In the embodiment described hereinabove, the non-revolution surface
is provided on the light exit surface side S0 of the second lens
L2, although the embodiment of the present invention is not limited
to this example. Even when a non-revolution surface as the lens
surface is provided on the light exit surface side of the first
lens L1, a generally equal illumination distribution can be
realized. The above-described non-revolution surface may be
provided on the light source side lens surface (light entry
surface) of the first lens L1 or the light source side lens surface
(light entry surface) of the second lens L2. Note that when a
non-revolution surface as the lens surface is provided on the light
entry surface of the first lens L1 and/or the second lens L2,
typically, the non-revolution surface forms a concave surface. In
this case, the above-described boundary lines B1 to B4 are formed
as trough lines in the lens surface.
As described above, in the lighting device 100 according to the
embodiment of the present invention, it is only necessary that a
non-revolution surface is formed at at least either of the lens
surfaces, the light entry surface or the light exit surface, of the
first lens L1 or the second lens L2. Note that all of the lens
surfaces may be a non-revolution surface, but in this case, there
is concern about increase in cost. Therefore, preferably, a
non-revolution surface is provided only on the light exit surface
side of the first lens L1 or the second lens L2. Further, providing
a non-revolution surface at least on the light exit surface of the
second lens L2 is advantageous for realizing a generally
quadrangular illumination distribution.
Embodiment 4-2
FIGS. 35(a) and 35(b) are a perspective view and cross-sectional
view showing a lighting device 200 of Embodiment 4-2. FIG. 35(c) is
a perspective view showing the shape of the light exit side surface
of a second lens L2.
The lighting device 200 includes a surface light source 1, a first
lens L1 provided on the light exit side of the surface light source
1, and a second lens L2 provided on the light exit side of the
first lens L1, as does the lighting device 100. The center of the
surface light source and the lens surface centers of the lenses L1,
L2 are aligned along the optical axis.
In the lighting device 200, the shape of a non-revolution surface
formed at the light exit surface of the second lens L2 is different
from that of the lighting device 100 of Embodiment 4-1. The surface
light source 1 and the form of the first lens L1 are the same as
those of the lighting device 100, and therefore, the description
thereof is herein omitted. In the following section, the lens
surface of the second lens L2 is described.
In this embodiment also, the second lens L2 generally has the shape
of a plano-convex lens. The light entry surface of the second lens
L2 is a flat surface. The light exit surface of the second lens L2
generally has a convex surface shape. Note that, however, in the
present embodiment, the light exit surface of the second lens L2 is
configured to include a non-revolution surface which is different
from that of Embodiment 4-1 as the lens surface.
The second lens L2 is a body of 3-fold rotational symmetry about an
axis extending through the center O of the lens surface and
perpendicular to the lens surface (typically, identical with the
optical axis). In this configuration, the light exit surface S0 of
the second lens L2 has three unit faces S1 to S3. The three unit
faces S1 to S3 are separated by three boundary lines B1 to B3
extending outward from the center O of the lens surface which is
placed on the optical axis. In the present embodiment, a
non-revolution surface including such three unit faces is used to
realize a spotlight which is capable of forming a generally
equilateral triangular illumination region.
Each of the three unit faces S1 to S3 is a free curved surface.
Each free curved surface has different curvatures in the x-axis
direction and the y-axis direction shown in FIG. 35(c). The three
unit faces S1 to S3 have substantially equal curvature
distributions and are symmetrically arranged about an axis
extending through the center O of the lens surface and parallel to
the z-axis direction shown in FIG. 35(a).
Next, the unit faces S1 to S3 are described more specifically.
Hereinafter, the unit face S1, which is one of the unit faces shown
in FIG. 35(c), is only described although the same description
applies to the other unit faces S2 and S3.
On the unit face S1, there are three points P1, P2, P3 which are
aligned in the y-direction shown in FIG. 35(c). The unit face S1 is
formed so as to satisfy the following formula:
Rx1.noteq.Rx2.noteq.Rx3 where Rx1, Rx2, Rx3 are the radii of
curvature in the x-direction at the points P1, P2, P3,
respectively.
Note that, in the embodiment shown in the drawing, the curved
surface is determined so as to satisfy the relationship of
Rx1>Rx2>Rx3, although this relationship is merely exemplary.
The present invention is not limited to this example. In some
cases, the curved surface may satisfy the relationship of
Rx1<Rx2<Rx3.
Also, the three points P1, P2, P3 are present on a curve which has
an equal curvature in the y-direction. At the respective points,
the curvatures in the y-direction are equal to one another.
On the other hand, as shown in FIG. 35(c), on the unit face S1,
there are three points Q1, Q2, Q3 which are aligned in the
x-direction. The unit face S1 is formed so as to satisfy the
following formula: Ry1.noteq.Ry2.noteq.Ry3 where Ry1, Ry2, Ry3 are
the radii of curvature in the y-direction at the three points Q1,
Q2, Q3, respectively.
In the embodiment shown in the drawing, the curved surface is
determined so as to satisfy the relationship of Ry1>Ry2>Ry3,
although this relationship is merely exemplary. The present
invention is not limited to this example. In some cases, the curved
surface may satisfy the relationship of Ry1<Ry2<Ry3.
Also, the three points Q1, Q2, Q3 are present on a curve which has
an equal curvature in the x-direction. At the respective points,
the curvatures in the x-direction are equal to one another.
That is, each of thick lines extending in the y-direction shown in
the drawing (e.g., curves extending through P1, P2, P3) is the set
of points which have different curvatures in the x-direction and
have equal curvatures in the y-direction. Each of thick lines
extending in the x-direction shown in the drawing (e.g., curves
extending through Q1, Q2, Q3) is the set of points which have
different curvatures in the y-direction and have equal curvatures
in the x-direction.
Next, a specific design of the above-described lens surface is
described.
Table 2 presented below shows the height in the z-direction at the
respective x, y coordinates (the lens thickness at the respective
points) over the unit face S1 in the x-y plane including the
x-direction and the y-direction in FIG. 35(c) (a plane orthogonal
to the optical axis). The lens height at the respective x, y
coordinates, z=f(x, y), is defined by, for example, the following
formula:
f(x,y)=-c.sub.yx.sup.2/(1+(1-(1+k)c.sub.y.sup.2x.sup.2).sup.1/2)-c.sub.xy-
.sup.2/(1+(1-c.sub.x.sup.2y.sup.2).sup.1/2)
Here, c.sub.y is 1/Ry, c.sub.x is 1/Rx, and k is the conic constant
(shown as "Conic" in Table 2). The lens height z is a value that is
obtained relative to the height at the lens center O which is zero
(0).
TABLE-US-00002 TABLE 2 Radius of Curvature Radius 348 918 286 258
228 198 168 199 108 78 48 of Cur- x vature Conic y -17.5 -15.75
-1.4 -12.25 -10.5 -8.75 -7 -5.25 -3.5 -17.5 0 53.992 1.5 -17.5
-3.49196 -2.91631 -2.43071 -2.03171 48.52 1.5 -15.75 -3.82187
-3.14158 -2.56848 -2.09463 -1.73613 49.732 1.5 -1.4 -4.22898
-3.42152 -2.74693 -2.1894 -1.73977 -1.394 39.628 1.5 -12.25 -4.7186
-3.75697 -2.9642 -2.31339 -1.78745 -1.3767 -1.07- 801 36.208 1.5
-10.5 -5.30017 -4.14289 -3.2133 -2.4602 -1.85409 -1.37756 -1.02-
168 33.472 1.5 -8.75 -5.9649 -4.56298 -3.47885 -2.61774 -1.93093
-1.39064 -0.9- 8116 -0.69594 31.42 1.5 -7 -6.68403 -4.98153
-3.73374 -2.76704 -2.00521 -1.40773 -0.9514- 7 -0.6242 80.052 1.5
-5.25 -7.37003 -5.3355 -3.93849 -2.88321 -2.06128 -1.41921 -0.9- 27
-0.56758 -0.33325 20.026 1.5 -3.5 -8.12067 -5.66537 -4.12158
-2.08681 -2.11354 -1.43465 -0.0- 1367 -0.52031 -0.2607 -0.13144
28.342 1.5 -1.75 -8.88701 -5.02835 -4.26235 -3.06633 -2.15532
-1.45010 -0.- 00920 -0.50825 -0.23230 -0.07370 28 1.5 0 -8.48566
-0.07894 -4.34143 -3.11202 -2.18113 -1.4027 -0.91214 -0.- 50351
-0.22093 -0.05482 0 28.342 1.5 1.75 -8.88701 -5.92895 -4.26135
-3.06633 -2.15532 -1.45019 -0.9- 0929 -0.50825 -0.23239 -0.07379
29.026 1.5 3.5 -5.12067 -5.66507 -4.22158 -2.98661 -2.12354
-1.43465 -0.91- 367 -0.52931 -0.2697 -0.13144 30.052 1.5 5.25
-7.37006 -5.3355 -3.93849 -2.88321 -2.06128 -1.41921 -0.92- 7
-0.58758 -0.93325 31.42 1.5 7 -6.68403 -4.98153 -3.73374 -2.76704
-2.00521 -1.40773 -0.95147- -0.6242 33.472 1.5 8.75 -5.9649
-4.56298 -3.47885 -2.61774 -1.93093 -1.39064 -0.98- 116 -0.69594
36.208 1.5 10.5 -5.30017 -4.14289 -3.2133 -2.4602 -1.85409 -1.37756
-1.021- 68 39.628 1.5 12.25 -4.7196 -3.75697 -2.9642 -2.31333
-1.78745 -1.3767 -1.078- 01 43.732 1.5 1.4 -4.22898 -3.42152
-2.74693 -2.1894 -1.73977 -1.394 48.52 1.5 15.75 -3.82187 -3.14158
-2.56848 -2.09463 -1.71613 53.992 1.5 17.5 -5.49186 -2.91631
-2.43071 -2.03171
FIG. 36(a) shows the illuminance distribution across an
illumination region realized by the lighting device 200. FIGS.
36(b) and 36(c) show a planar shape of the projected light (spot
shape projected on the screen). Note that FIG. 36(b) shows a spot
shape obtained from the design values of the optical system. FIG.
36(c) shows a spot shape obtained using an actually manufactured
optical system.
As shown in the drawings, by providing a lens surface of a
non-revolution surface consisting of the above-described three free
curved surfaces at the light exit surface of the second lens L2, a
generally equilateral triangular spot shape can be realized. In the
present embodiment, light from the light source is refracted by the
lens surface such that the light is converged into an equilateral
triangular shape without blocking part of the light from the light
source by a light blocking member, the light utilization efficiency
can be improved.
As a result of a calculation by simulation, it was confirmed that
according to the lighting device of the present embodiment the
light utilization efficiency of the light reaching an illumination
region which is 1 m ahead is about 80%.
In this embodiment also, the above-described first lens L1 or
second lens L2 may be made of the same material as that of
Embodiment 1. In the embodiment which has been described above, a
non-revolution surface is provided on the light exit surface side
S0 of the second lens L2, although the present invention is not
limited to this example. It is only necessary that a non-revolution
surface is formed at at least either of the lens surfaces, the
light entry surface or the light exit surface, of the first lens L1
or the second lens L2.
Embodiment 4-3
FIGS. 37(a) and 37(b) are a perspective view and cross-sectional
view showing a lighting device 300 of Embodiment 4-3. FIG. 37(c) is
a perspective view showing the shape of the light exit side surface
of a second lens L2.
The lighting device 300 includes a surface light source 1, a first
lens L1 provided on the light exit side of the surface light source
1, and a second lens L2 provided on the light exit side of the
first lens L1, as does the lighting device 100. The center of the
surface light source and the lens surface centers of the lenses L1,
L2 are aligned along the optical axis.
In the lighting device 300, the shape of a non-revolution surface
formed at the light exit surface of the second lens L2 is different
from that of the lighting device 100 of Embodiment 4-1. The surface
light source 1 and the form of the first lens L1 are the same as
those of the lighting device 100, and therefore, in the following
section, only the lens surface of the second lens L2 is
described.
In this embodiment also, the second lens L2 generally has the shape
of a plano-convex lens. The light entry surface of the second lens
L2 is a flat surface. The light exit surface of the second lens L2
generally has a convex surface shape.
The second lens L2 is a body of 5-fold rotational symmetry about an
axis extending through the center O of the lens surface and
perpendicular to the lens surface (typically, conformable to the
optical axis). In this configuration, the light exit surface S0 of
the second lens L2 has ten unit faces which are separated by five
boundary lines (ridge lines) B1a to B5a extending outward from the
center O of a lens surface and five boundary lines (trough lines)
B1b to B5b extending outward from the center O of another lens
surface. The five boundary lines (ridge lines) and the five
boundary lines (trough lines) are alternately arranged. Each unit
face is provided between one boundary line (ridge line) and one
boundary line (trough line). In the present embodiment, a
non-revolution surface including such ten unit faces is used to
realize a spotlight which is capable of forming a generally
star-like shaped illumination region.
Each of the ten unit faces is a free curved surface. In this free
curved surface, the curvatures in the directions of two
mutually-orthogonal axes which are defined in a plane parallel to
the lens surface are different. Of the ten unit faces, two unit
faces lying at both sides of one boundary line (e.g., two unit
faces S1 and S2 lying at both sides of the boundary line B1a in
FIG. 37(c)) have a symmetrical shape about a plane extending
through the boundary line and parallel to the z-direction. In the
present embodiment, when considering these two unit faces as a pair
of unit faces, five pairs of unit faces are symmetrically arranged
about an axis extending through the center O of the lens surface
and parallel to the z-direction.
FIGS. 38(a-1) and 38(b-1) show two types of the second lens L2
which have ten unit faces (free curved surfaces) but have different
curved surface shapes in the unit faces. FIGS. 38(a-2) and 38(b-2)
show the shapes of the illumination region in the case where the
second lens L2 is used. As shown in FIGS. 38(a-2) and 38(b-2), no
matter which lens is used, a star-like spot shape can be realized.
Note that, as a result of a calculation by simulation, it was
confirmed that according to the lighting device of the present
embodiment the light utilization efficiency of the light reaching
an illumination region which is 1 m ahead is about 77%.
As seen from FIGS. 38(a-2) and 38(b-2), the shape of the
illumination region (the distribution of projected light) can be
changed by changing the shape of the free curved surfaces that form
the unit faces. Therefore, the shape of the free curved surfaces
may be appropriately adjusted such that a desired shape of the
illumination region can be obtained.
Further, as illustrated in Embodiments 4-1, 4-2 which have been
described above and Embodiment 4-3 described in this section, no
matter which of the generally square shape, the generally
equilateral triangular shape, and the generally star-like shape the
illumination region has, the shape of the illumination region can
also be made highly symmetrical by arranging curved surfaces
symmetrically about the lens center O in the non-revolution
surface.
Note that, in the present embodiment also, the above-described
first lens L1 or second lens L2 may be made of the same material as
that of Embodiment 1. In the embodiment which has been described
above, a non-revolution surface as the lens surface is provided on
the light exit surface side SO of the second lens L2, although the
present invention is not limited to this example. It is only
necessary that a non-revolution surface is formed at at least
either of the lens surfaces, the light entry surface or the light
exit surface, of the first lens L1 or the second lens L2.
Embodiment 4-4
FIGS. 39(a) and 39(b) are a perspective view and cross-sectional
view showing a lighting device 400 of Embodiment 4-4. FIG. 39(c) is
a perspective view showing the shape of the light exit side surface
of a second lens L2.
The lighting device 400 includes a surface light source 1, a first
lens L1 provided on the light exit side of the surface light source
1, and a second lens L2 provided on the light exit side of the
first lens L1, as does the lighting device 100. The center of the
surface light source and the lens surface centers of the lenses L1,
L2 are aligned along the optical axis.
In the lighting device 400, the shape of a non-revolution surface
formed at the light exit surface of the second lens L2 is different
from that of the lighting device 100 of Embodiment 4-1. The surface
light source 1 and the form of the first lens L1 are the same as
those of the lighting device 100, and therefore, in the following
section, only the lens surface of the second lens L2 is
described.
In this embodiment also, the second lens L2 generally has the shape
of a plano-convex lens. The light entry surface of the second lens
L2 is a flat surface. The light exit surface of the second lens L2
generally has a convex surface shape.
The second lens L2 is a body of 5-fold rotational symmetry about an
axis extending through the center O of the lens surface and
perpendicular to the lens surface (typically, conformable to the
optical axis). In this configuration, the light exit surface SO of
the second lens L2 has ten unit faces which are separated by five
major boundary lines (trough lines) B1a to B5a extending outward
from the center O of the lens surface which is placed on the
optical axis and five minor boundary lines (trough lines) B1b to
B5b extending outward from intermediate positions on the major
boundary lines B1a to B5a.
In a region lying between two adjacent major boundary lines (e.g.,
the major boundary line B1a and the major boundary line B2a shown
in the drawing), there are two types of unit faces S1, S2 which are
separated by one minor boundary line (e.g., the minor boundary line
B1b shown in the drawing). These two types of unit faces S1, S2
have different areas and different shapes.
Considering these two types of unit faces as a pair, five pairs of
unit faces are rotationally symmetrically arranged about the
optical axis.
In Embodiments 4-1 to 4-3 that have been described above, adjacent
free curved surfaces (unit faces) have an identical shape or are in
symmetry about a cross section including a boundary line, while in
Embodiment 4-4 the above-described two types of unit face have
totally different shapes. Even when a lens of such a shape is used,
light can be projected onto a desired region while maintaining high
light utilization efficiency.
FIG. 40(a) shows an illuminance distribution across an illumination
region produced by the lighting device 400. FIG. 40(b) shows a
planar shape of projected light. Note that FIG. 40(a) separately
shows the graphs of the illuminance distributions along the
horizontal direction X and the vertical direction Y shown in FIG.
40(b). As seen from the drawing, the lighting device of the present
embodiment is capable of forming a spot shape in the form of a
whirlpool. Note that, as a result of a calculation by simulation,
it was confirmed that according to the lighting device of the
present embodiment the light utilization efficiency of the light
reaching an illumination region which is 1 m ahead is about
79%.
Note that, in the present embodiment also, the above-described
first lens L1 or second lens L2 may be made of the same material as
that of Embodiment 1. In the embodiment which has been described
above, a non-revolution surface as the lens surface is provided on
the light exit surface side SO of the second lens L2, although the
present invention is not limited to this example. It is only
necessary that a non-revolution surface is formed at at least
either of the lens surfaces, the light entry surface or the light
exit surface, of the first lens L1 or the second lens L2.
Embodiment 4-5
FIGS. 41(a) and 41(b) are a perspective view and cross-sectional
view showing a lighting device 500 of Embodiment 4-5. FIG. 41(c) is
a perspective view showing the shape of the light exit side surface
of a second lens.
The lighting device 500 includes a surface light source 1, a first
lens L1 provided on the light exit side of the surface light source
1, and a second lens L2 provided on the light exit side of the
first lens L1, as does the lighting device 100. The center of the
surface light source and the lens surface centers of the lenses L1,
L2 are aligned along the optical axis.
In the lighting device 500, the shape of a non-revolution surface
formed at the light exit surface of the second lens L2 is different
from that of the lighting device 100 of Embodiment 4-1. The surface
light source 1 and the form of the first lens L1 are the same as
those of the lighting device 100, and therefore, in the following
section, only the lens surface of the second lens L2 is
described.
In this embodiment also, the second lens L2 generally has the shape
of a plano-convex lens. The light entry surface of the second lens
L2 is a flat surface. The light exit surface of the second lens L2
generally has a convex surface shape.
The second lens L2 is a body of 2-fold rotational symmetry about an
axis extending through the center O of the lens surface and
perpendicular to the lens surface (typically, conformable to the
optical axis).
In this configuration, the light exit surface SO of the second lens
L2 has four unit faces S1 to S4 which are separated by four
boundary lines B1 to B4 extending outward from the center O of the
lens surface which is placed on the optical axis.
Of the unit faces S1 to S4, two unit faces opposing each other
relative to the lens center O (the unit face S1 and the unit face
S3, or the unit face S2 and the unit face S4) are curved surfaces
which have equal curvatures. However, adjacent lens surfaces (e.g.,
the unit face S1 and the unit face S2) are curved surfaces which
have different curvatures. In the present embodiment, a lens whose
lens surface is a non-revolution surface including four unit faces
of such 2.times.2 types is used to realize a spotlight which is
capable of forming a generally-rectangular illumination region.
Each of the four unit faces S1 to S4 is a free curved surface. Each
free curved surface has different curvatures in the x-axis
direction and the y-axis direction shown in FIG. 41(a). As
described above, since opposing unit faces are equal curved
surfaces, they have equal curvatures in the axial direction.
Meanwhile, since adjacent unit faces are different curved surfaces,
they have different curvatures. Hereinafter, a more specific design
of the lens surface is described.
Table 3 and Table 4 presented below respectively show the design of
the curvature set for the unit faces S1, S3 (Table 3) and the
design of the curvature set for the unit faces S2, S4 (Table 4). As
shown in the tables, the parameters of the design are different for
the respective unit faces. Note that the meaning of numbers shown
in the tables (height z in x-y coordinates) is the same as the
examples shown in Table 1 and Table 2, and therefore, the
description thereof is herein omitted.
TABLE-US-00003 TABLE 3 Radius of Curvature Radius 54 53.4 52.8 52.2
51.6 51 50.4 49.8 49.2 48.6 48 of Cur- x vature Conic y -17.5
-15.75 -14 -12.25 -10.5 -8.75 -7 -5.25 -3.5 -1.75 0 53.002 1.5
-17.6 -5.06506 -6.38336 -4.83207 -4.26835 -4.10440 40.52 1.5 15.75
5.01019 5.12600 4.54129 4.04620 3.60095 43.732 1.5 -1.4 -5.78304
-4.96107 -4.23099 -3.7217 -3.24500 -2.85763 36.628 1.5 -2.25
-5.91175 -4.945 -4.14426 -3.28014 -2.93331 -2.49045 -2.14- 218
36.208 1.5 -10.5 -6.1124 -5.01197 -4.07639 -3.31299 -2.69179
-2.19154 -1.7- 9912 33.472 1.5 -8.75 -6.56851 -5.16433 -4.07596
-3.20791 -2.51026 -1.95343 -1.- 5185 -1.19298 31.42 1.5 -7 -7.06925
-5.36526 -4.11473 -3.14554 -2.37474 -1.76663 -1.2940- 5 -0.94097
-0.69699 30.052 1.5 -5.25 -7.58624 -5.55086 -4.15229 -3.09447
-2.26861 -1.62063 -1.- 11913 -0.74518 -0.48648 29.026 1.5 -3.5
-8.21661 -5.76063 -4.21645 -3.08054 -2.20551 -1.52396 -0.9- 9888
-0.60806 -0.33762 -0.17907 28.342 1.5 -1.75 -8.91098 -5.95272
-4.23605 -3.08979 -2.17828 -1.47249 -3.- 93057 -0.52791 -0.24934
-0.03567 28 1.5 0 -9.48536 -6.07994 -4.34143 -3.11205 -2.18118
-1.4627 -3.81214 -0.- 50351 -0.22093 -0.05482 0 28.942 1.5 1.75
-8.91098 -5.95272 -4.23605 -3.08979 -2.17828 -1.47249 -0.9- 3057
-0.52791 -0.24934 -0.03567 29.026 1.5 3.5 -8.21661 -5.76063
-4.21615 -3.08054 -2.20551 -1.52396 -0.99- 888 -0.60806 -0.33762
-0.17907 30.052 1.5 5.25 -7.58624 -5.55086 -4.15220 -3.00447
-2.26861 -1.62053 -1.1- 1013 -0.74618 -0.48648 31.42 1.5 7 -7.00925
-5.30520 -4.11473 -3.14504 -2.37474 -1.70003 -1.29400- -0.94097
-0.09099 33.472 1.5 8.75 -6.56851 -5.16433 -4.07590 -3.20791
-2.51026 -1.95343 -1.5- 185 -1.19298 36.208 1.5 10.5 -0.1124
-5.01197 -4.07639 -3.31239 -2.69179 -2.19154 -1.29- 912 39.628 1.5
12.25 -5.91175 -4.945 -4.14426 -3.28014 -2.93331 -2.49045 -2.14-
218 43.732 1.5 1.4 -5.79304 -4.98107 -4.29633 -3.7217 -3.24506
-2.85763 46.52 1.5 15.75 -5.81319 -5.12683 -4.54129 -4.04623
-3.63395 53.992 1.5 17.5 -5.96596 -5.38336 -4.83297 -4.45835
-4.10448
TABLE-US-00004 TABLE 4 Radius of Curvature 54 53.4 52.8 52.2 51.0
51 50.4 49.8 49.2 48.0 48 Radius of y Curvature Conic x -17.5
-15.75 -14 -12.25 -10.5 -8.75 -7 -5.25 -3.5 -1.75 - 0 80.983 1.5
-1.75 72.78 1.5 -15.75 65.593 1.5 -14 59.442 1.5 -12.25 54.312 1.5
-10.5 50.203 1.5 -8.75 -4.0387 -3.36621 47.13 1.5 -7 -4.04669
-3.30799 -2.67482 45.073 1.5 -5.25 -4.0524 -3.25996 -2.5854
-2.01401 -1.5352 43.539 1.5 -3.5 -4.08284 -3.24463 -2.53496
-1.93569 -1.43465 -1.02287 - 42.513 1.5 -1.75 -4.12923 -3.25168
-2.51605 -1.80678 -1.37005 -0.05560 -0.- 6168 -0.36307 42 1.5 0
-4.10117 -3.2717 -2.52279 -1.89312 -1.30821 -0.93702 -0.59583 -0.-
33139 -0.14047 -0.0305 0 42.513 1.5 1.75 -4.12823 -3.25158 -2.51605
-1.69078 -1.37995 -0.85509 -0.6- 168 -0.35307 43.639 1.5 3.5
-4.38284 -3.24483 -2.53496 -1.93569 -1.43465 -1.02287 45.073 1.5
5.25 -4.0524 -3.25986 -2.5854 -2.01401 -1.5352 47.13 1.5 7 -4.04663
-3.30739 -2.67482 50.203 1.5 8.75 -4.0387 -3.36621 54.312 1.5 10.5
59.442 1.5 12.25 65.593 1.5 14 72.78 1.5 15.75 80.983 1.5 17.6
FIG. 42(a) shows an illuminance distribution across an illumination
region produced by the lighting device 500. FIG. 42(b) shows a
planar shape of projected light. Note that FIG. 42(a) separately
shows the graphs of the illuminance distributions along the
horizontal direction X and the vertical direction Y shown in FIG.
42(b).
As shown in FIG. 42(b), a lens surface of a non-revolution surface
consisting of the above-described four free curved surfaces of
2.times.2 types is provided at the light exit surface of the second
lens L2, whereby a generally rectangular spot shape can be
realized. Note that, as a result of a calculation by simulation, it
was confirmed that according to the lighting device 500 of the
present embodiment the light utilization efficiency of the light
reaching an illumination region which is 1 m ahead is about
80%.
Note that, in the present embodiment also, the above-described
first lens L1 or second lens L2 may be made of the same material as
that of Embodiment 1. In the embodiment which has been described
above, a non-revolution surface as the lens surface is provided on
the light exit surface side SO of the second lens L2, although the
present invention is not limited to this example. It is only
necessary that a non-revolution surface is formed at at least
either of the lens surfaces, the light entry surface or the light
exit surface, of the first lens L1 or the second lens L2.
Embodiment 4-6
FIGS. 43(a) and 43(b) are a perspective view and cross-sectional
view showing a lighting device 600 of Embodiment 4-6. FIG. 44(a)
shows an illuminance distribution across an illumination region
produced by the lighting device 600. FIG. 44(b) shows a planar
shape of projected light. Note that FIG. 44(a) shows the graph of
the illuminance distribution along the horizontal direction X shown
in FIG. 44(b).
The lighting device 600 of the present embodiment includes a
surface light source 1, a first lens L1 provided on the light exit
side of the surface light source 1, and a second lens L2 provided
on the light exit side of the first lens L1, as does the lighting
device 100. The center of the surface light source 1 and the lens
surface centers of the lenses L1, L2 are aligned along the optical
axis.
In the lighting device 600, the shape of a non-revolution surface
formed at the light exit surface of the second lens L2 is different
from that of the lighting device 100 of Embodiment 4-1. The surface
light source 1 and the form of the first lens L1 are the same as
those of the lighting device 100, and therefore, in the following
section, only the lens surface of the second lens L2 is
described.
In this embodiment also, the second lens L2 generally has the shape
of a plano-convex lens. The light entry surface of the second lens
L2 is a flat surface. The light exit surface of the second lens L2
generally has a convex surface shape. The second lens L2 is a body
of 4-fold rotational symmetry about an axis extending through the
center O of the lens surface and perpendicular to the lens surface
(typically, conformable to the optical axis). In this
configuration, the light exit surface SO of the second lens L2 has
four unit faces S1 to S4 which are separated by four boundary lines
B1 to B4 extending outward from the center O of the lens surface
which is placed on the optical axis. In the present embodiment, a
non-revolution surface including such four unit faces is used to
realize a spotlight which is capable of forming a generally square
illumination region.
Each of the four unit faces S1 to S4 is formed by a toroidal
surface, which is different from that of the lighting device 100 of
Embodiment 4-1. This toroidal surface has different curvatures in
the x-axis direction and the y-axis direction shown in FIGS. 43(a)
and 43(b). The four unit faces S1 to S4 have substantially equal
curvature distributions and are symmetrically arranged about an
axis extending through the center O of the lens surface and
parallel to the z-axis direction.
Now, the toroidal surface is described. When described as to the
unit face S1 shown in the drawing, the toroidal surface refers to a
surface which has different curvatures in the x-direction and the
y-direction.
Note that, although the free curved surface (unit face) of the lens
of Embodiment 1 also has different curvatures in the x-direction
and the y-direction, the toroidal surface used in this embodiment
is different from the free curved surface of Embodiment 1 in that
an arc is formed in either of the cross section along the
x-direction or the y-direction. In the case of the toroidal
surface, the curved surface can be defined only by the radius of
curvature in the x-direction, Rx, and the radius of curvature in
the y-direction, Ry.
In the present embodiment, the radius of curvature in the
x-direction, Rx, is set to, for example, a value which is not less
than a half of the effective diameter of the second lens L2 and not
more than three times the effective diameter of the second lens L2.
The radius of curvature in the y-direction, Ry, is set to, for
example, a value which is not less than Rx and not more than five
times Rx.
As shown in FIGS. 44(a) and 44(b), a generally square spot shape
with rounded vertexes can be realized using the lighting device 600
of the present embodiment. Further, the illuminance distribution
across the illumination region can be uniform. Further, as a result
of a calculation by simulation, it was confirmed that according to
the lighting device 600 of the present embodiment the light
utilization efficiency of the light reaching an illumination region
which is 1 m ahead is about 81%.
Next, as a variation of the present embodiment, an embodiment of
forming a generally equilateral triangular illumination region
using a lens which has a non-revolution surface consisting of three
toroidal surfaces is described.
FIGS. 45(a) and 45(b) are a perspective view and cross-sectional
view showing a lighting device 650 of the present embodiment. FIG.
46(a) shows an illuminance distribution across an illumination
region produced by the lighting device 650. FIG. 46(b) shows a
planar shape of projected light. Note that FIG. 46(a) separately
shows the graphs of the illuminance distributions along the
horizontal direction X and the vertical direction Y shown in FIG.
46(b).
In the lighting device 650, the second lens L2 is a body of 3-fold
rotational symmetry about an axis extending through the center O of
the lens surface and perpendicular to the lens surface (typically,
conformable to the optical axis). In this configuration, the light
exit surface S0 of the second lens L2 has three unit faces S1 to S3
which are separated by three boundary lines B1 to B3 extending
outward from the center O of the lens surface which is placed on
the optical axis.
Each of the three unit faces S1 to S3 is formed by a toroidal
surface. The three unit faces S1 to S3 are symmetrically arranged
about an axis extending through the center O of substantially the
same lens surface and parallel to the z-axis direction shown in the
drawing. Note that the radii of curvature Rx, Ry which define the
toroidal surface may be in the same ranges as those described
above.
As shown in FIG. 46(b), in the present embodiment, a generally
equilateral triangular spot shape with rounded vertexes can be
realized. Note that, as a result of a calculation by simulation, it
was confirmed that according to the lighting device of the present
embodiment the light utilization efficiency of the light reaching
an illumination region which is 1 m ahead is about 81%.
Note that, in the present embodiment also, the above-described
first lens L1 or second lens L2 may be made of the same material as
that of Embodiment 1. In the embodiment which has been described
above, a non-revolution surface as the lens surface is provided on
the light exit surface side SO of the second lens L2, although the
present invention is not limited to this example. It is only
necessary that a non-revolution surface is formed at at least
either of the lens surfaces, the light entry surface or the light
exit surface, of the first lens L1 or the second lens L2.
Embodiment 4-7
FIGS. 47(a) and 47(b) are a perspective view and cross-sectional
view showing a lighting device 700 of Embodiment 4-7. FIG. 48(a)
shows an illuminance distribution across an illumination region
produced by the lighting device 700. FIG. 48(b) shows a planar
shape of projected light. Note that FIG. 48(a) shows the graph of
the illuminance distribution along the horizontal direction X shown
in FIG. 48(b).
The lighting device 700 of the present embodiment includes a
surface light source 1, a first lens L1 provided on the light exit
side of the surface light source 1, and a second lens L2 provided
on the light exit side of the first lens L1, as does the lighting
device 100. The center of the surface light source 1 and the lens
surface centers of the lenses L1, L2 are aligned along the optical
axis.
In the lighting device 700, a non-revolution surface including four
cylindrical surfaces as the unit faces is provided over the lens
surface formed at the light exit surface of the second lens L2. The
other components are the same as those of the lighting device 600
of Embodiment 4-6, and therefore, detailed description thereof is
herein omitted.
Now, the cylindrical surface is described. When described as to the
unit face S1 shown in the drawing, the cylindrical surface refers
to a surface corresponding to a lateral surface of a cylinder which
has a curvature only in the x-direction but does not have a
curvature in the y-direction. Note that when described as to the
unit face S2 which is adjacent to the unit face S1, it has a
curvature only in the y-direction but does not have a curvature in
the x-direction. The shape of the cylindrical surface can be
defined by the radius of curvature R. The radius of curvature R is
set to, for example, a value which is not less than a half of the
effective diameter of the second lens L2 and not more than three
times the effective diameter of the second lens L2.
As shown in FIGS. 48(b) and 48(c), in the present embodiment, a
generally square spot shape with rounded vertexes can be realized.
Note that, as a result of a calculation by simulation, it was
confirmed that according to the lighting device of the present
embodiment the light utilization efficiency of the light reaching
an illumination region which is 1 m ahead is about 81%.
Also, it was confirmed that, particularly in the case where the
lens surface is configured using cylindrical surfaces, incidental
illumination regions are formed near each vertex of the square as
shown in FIGS. 48(b) and 48(c). When a non-revolution surface
including a plurality of unit faces is thus formed at the lens
surface, specific illumination portions which emerge in a
non-concentric shape in the illumination region are sometimes
observed, although such would not occur in the case where an
optical axis rotational surface is formed in a common optical
system.
Next, as a variation of the present embodiment, an embodiment of
forming a generally equilateral triangular illumination region
using a lens which has a non-revolution surface consisting of three
cylindrical surfaces is described.
FIGS. 49(a) and 49(b) are a perspective view and cross-sectional
view showing a lighting device 750 of the present embodiment. FIG.
49(c) is a plan view showing the second lens L2. FIG. 50(a) shows
an illuminance distribution across an illumination region produced
by the lighting device 750. FIG. 50(b) shows a planar shape of
projected light. Note that FIG. 50(a) separately shows the graphs
of the illuminance distributions along the horizontal direction X
and the vertical direction Y shown in FIG. 50(b).
In the lighting device 750, the second lens L2 is a body of 3-fold
rotational symmetry about an axis extending through the center O of
the lens surface and perpendicular to the lens surface (typically,
conformable to the optical axis). In this configuration, the light
exit surface SO of the second lens L2 has three unit faces S1 to S3
which are separated by three boundary lines B1 to B3 extending
outward from the center O of the lens surface which is placed on
the optical axis. In the present embodiment, a non-revolution
surface including such three unit faces is used to realize a spot
shape in which the illumination region has a generally equilateral
triangular shape.
Each of the three unit faces S1 to S3 is formed by a cylindrical
surface. The three unit faces S1 to S3 are symmetrically arranged
about an axis extending through the center O of substantially the
same lens surface and parallel to the z-axis direction shown in the
drawing. FIG. 49(c) shows the axial direction of the cylinder which
defines the cylindrical surface. The radius of curvature R which
defines the cylindrical surface may be in the same range as that
described above.
As shown in FIGS. 50(b) and 50(c), in the present embodiment, a
generally equilateral triangular spot shape with rounded vertexes
can be realized. Note that, as a result of a calculation by
simulation, it was confirmed that according to the lighting device
of the present embodiment the light utilization efficiency of the
light reaching an illumination region which is 1 m ahead is about
81%. In this variation also, it was confirmed that incidental
illumination regions are formed near each vertex of the equilateral
triangle as shown in FIGS. 50(b) and 50(c).
In the present embodiment also, the above-described first lens L1
or second lens L2 may be made of the same material as that of
Embodiment 1. In the embodiment which has been described above, a
non-revolution surface as the lens surface is provided on the light
exit surface side SO of the second lens L2, although the present
invention is not limited to this example. It is only necessary that
a non-revolution surface is formed at at least either of the lens
surfaces, the light entry surface or the light exit surface, of the
first lens L1 or the second lens L2.
Embodiment 4-8
FIGS. 51(a) and 51(b) are a perspective view and cross-sectional
view showing a lighting device 800 of Embodiment 4-8. The lighting
device 800 of the present embodiment uses a composite lens L12 in
place of the first lens L1 and the second lens L2 that have been
described in Embodiment 4-1. The composite lens L12 includes a
first lens portion L1' which has substantially the same function as
the first lens L1 and a second lens portion L2' which has
substantially the same function as the second lens L2.
The composite lens L12 has such a structure that the light exit
surface of the first lens L1 and the light entry surface of the
second lens L2 are joined together at about the centers of the
lenses.
The shape of the light exit surface of the composite lens L12 may
be the same as that of the light exit surface of the second lens
L2. That is, the light exit surface of the composite lens L12
includes four free curved surfaces (unit faces) separated by
boundary lines. These free curved surfaces are rotationally
symmetrically arranged about the optical axis. Each free curved
surface has different curvatures in the x-direction and the
y-direction that are orthogonal to each other.
The composite lens L12 having such a structure may be formed of a
material such as a resin by integral molding according to a known
method. Alternatively, the composite lens L12 may be manufactured
by separately producing the first lens L1 and the second lens L2
using the same material and then joining the produced lenses
together. In this case, when the first lens L1 and the second lens
L2 are joined together using the same material as the first lens L1
and the second lens L2, a difference in refractive index would not
occur, and therefore, reflection at the interface can be
prevented.
Note that, however, the composite lens L12 may be manufactured by
separately producing the first lens L1 and the second lens L2 using
different materials and then appropriately joining the produced
lenses together. In this case, the first lens and the second lens
can be made of materials which have different refractive indices,
and therefore, the design flexibility can be improved.
FIG. 52(a) shows a cross sectional of an example of the composite
lens L12. FIG. 52(b) enlargedly shows a portion around the first
lens portion L1'. As shown in FIGS. 52(a) and 52(b), the respective
sizes are set such that light from the light source 1 can be
efficiently converged by the first lens portion L1' and projected
onto a generally square region by the second lens portion L2'.
Therefore, an illumination region of a different shape can be
formed with high light utilization efficiency.
In the embodiment shown in FIG. 52(b), the joint width of the light
exit surface of the first lens portion L1' and the light entry
surface of the second lens portion L2' is set to 10.0 mm. If this
joint width is excessively large relative to the diameter of the
first lens portion (24.0 mm), there is a probability that the light
converging characteristic of the first lens portion deteriorates.
If the aforementioned joint width is excessively small, the
composite lens L12 can be readily broken. Thus, it is preferred
that the joint width is not less than 2 mm, for example, and the
ratio of the joint width to the diameter of the first lens portion
is not more than 30%, for example. If the joint width is narrower
than 2 mm, the probability of breakage increases when excessively
large stress is applied on the first lens portion L1'.
Table 5 presented below shows the design of the curvature set for
the unit faces S1 to S4. Note that the meaning of numbers shown in
Table 5 (height z in x-y coordinates) is the same as the examples
shown in Table 1 to Table 4, and therefore, the description thereof
is herein omitted.
TABLE-US-00005 TABLE 5 Radius of Curvature Radius of 38.8 57.4 56
54.6 53.2 51.8 50.4 49 47.6 46.2 44.8 Curvature Conic y -32.7 -29.4
-26.1 -22.9 -19.6 -16.3 -13.1 -9.8 -6.53 -3.- 27 -0 95.1851 1
-32.6667 -15.9 84.9707 1 -29.4 -14.7 -13.5 76.0331 1 -26.1333 -13.9
-12.5 -11.3 68.3723 1 -22.8667 -13.6 -11.8 -10.3 -9.08 61.9883 1
-19.6 -13.7 -11.5 -9.65 -8.19 -7.01 56.8811 1 -16.3333 -14.2 -11.4
-9.26 -7.54 -6.17 -5.09 53.0507 1 -13.0667 -15 -11.6 -9.04 -7.08
-5.54 -4.32 -3.38 50.4971 1 -9.8 -15.9 -11.8 -8.91 -6.74 -5.05
-3.73 -2.71 -1.96 48.5819 1 -6.53333 -17.1 -12.1 -8.91 -6.56 -4.74
-3.33 -2.25 -1.45 -0.39 - 47.3051 1 3.26667 18.7 12.5 8.98 6.49
4.59 3.11 1.99 1.15 0.57 0.23 46.6667 1 -4.4E-15 -20 -12.7 -9.09
-6.51 -4.56 -3.06 -1.91 -1.05 -0.46 -0.- 11 -0 47.3051 1 3.266667
-18.7 -12.5 -8.98 -6.49 -4.59 -3.11 -1.99 -1.15 -0.57 -- 0.23
48.5819 1 6.533333 -1.71 -12.1 -8.91 -6.56 -4.74 -3.33 -2.25 -1.45
-0.89 - 50.4971 1 9.8 -15.9 -11.8 -8.91 -6.74 -5.05 -3.73 -2.71
-1.96 53.0507 1 3.06667 -15 -11.6 -9.04 -7.08 -5.54 -4.32 -3.33
56.8811 1 6.33333 -14.2 -11.4 -9.26 -7.54 -6.17 -5.09 61.9883 1
19.0 -13.7 -11.5 -9.05 -8.19 -7.01 68.3723 1 22.86667 -13.6 -11.8
-10.3 -9.08 76.0331 1 26.13333 13.9 12.5 11.3 84.9707 1 29.4 -14.7
-13.5 95.1851 1 32.66667 -15.9
As shown in FIGS. 53(a) and 53(b), a generally square spot shape
can be realized using the lighting device 800 of the present
embodiment. Further, the illuminance distribution across the
illumination region can be uniform. Further, as a result of a
calculation by simulation, it was confirmed that according to the
lighting device 800 of the present embodiment the light utilization
efficiency of the light reaching an illumination region which is 1
m ahead is about 80%.
Thus, since the lighting device 800 uses the lens 12 in which the
first lens portion L1' and the second lens portion L2' are
integrated together, alignment and fixing of the lens 12 relative
to the light source can be more readily achieved.
Although the embodiments of the present invention have been
described above, as a matter of course, various modifications are
possible. For example, by providing a non-revolution surface at the
lens surface of the first lens or the second lens so as to include
the above-described lens shape which is capable of forming a
quadrangular spot shape and the above-described lens shape which is
capable of forming a triangular spot shape, light can be projected
onto a home plate shape (or arrow shape) region with high
illuminance uniformity. Alternatively, it is also possible to form
an illumination region of a different shape, such as a heart shape
or the like. Thus, in a device according to an embodiment of the
present invention, a non-revolution surface including a plurality
of unit faces separated by boundary lines which have varying
curvatures is formed at the lens surface, whereby a non-circular
spot shape can be realized while high illuminance uniformity is
achieved.
The present invention is not limited to the above-described
embodiments but can be variously modified within the scope of the
claims. An embodiment which is realized by an appropriate
combination of technical features disclosed in different
embodiments falls within the technical scope of the present
invention.
INDUSTRIAL APPLICABILITY
A lighting device according to an embodiment of the present
invention is applicable to a wide variety of lighting products,
including lighting devices which are configured to illuminate only
a narrow area, such as spotlights, light projectors, or the like,
lighting devices which are configured to uniformly illuminate a
somewhat large area, such as streetlights, reading lights, indoor
indirect lighting devices, vehicle interior roof lights, or the
like, vehicle headlights which are configured to emit a larger
amount of light, etc. Also, the lighting device can be suitably
used as a spotlight which is capable of forming a non-circular
illumination region for use in stage lighting devices.
The emission wavelength of the light source is not limited to
visible light. The light source can be used for light sources for
use in infrared sensors which use infrared light, spot exposure
lamps and sterilization lamps which use ultraviolet light, etc.
REFERENCE SIGNS LIST
1 light source (light emission section) 2 optical lens section 3
optical lens 4 optical lens 5 opening section 11 lighting device 12
lighting device 13a lighting device 13b lighting device 22 optical
lens section 23 optical lens section AX optical axis L1 optical
lens (first lens) L2 optical lens (second lens) f1 first focal
position f2 second focal position F1 focal point of first lens F2
focal point of second lens 100-800 lighting device
* * * * *